Skip to main content

Full text of "Anatomy of the human body"

See other formats


^^sr^T/e  ^^^^uv/Ci/^>e        O^i^zE    Ai^G/cjc^A^    Jc 


f-toO^ 


UNIVERSITY  OF  CALIFORNIA 

MEDICAL  CENTER  LIBRARY 

SAN  FRANCISCO 


GIFT  OF 
LESTER  J.   SAWYER,  M.D. 


Digitized  by  the  Internet  Archive 

in  2007  with  funding  from 

IVIicrosoft  Corporation 


http://www.archive.org/details/anatomyofhumanboOOgrayrich 


ANATOMY 


OF 


THE  HUMAN  BODY 


BY 


henry/qbay,  f.r.s. 

FELLOW    OF    THE    KOYAL    COLLEGE    OF    STJHg^NS  ;    LECTURER    ON    ANATOMY    AT   ST.    GEORGE's 
HOSPITAL    MEDICAL    SCHOOL,    LONDON 


TWENTIETH  EDITION 

THOROUGHLY  REVISED  AND  RE-EDITED 
BY 

WARREN  H.  LEWIS,  B.S.,  M.D. 

PROFESSOR    OF   PHYSIOLOGICAL    ANATOMY,    JOHNS    HOPKINS  UNIVERSITY,    BALTIMORE,   MD. 


lUu0tratc^  witb  1247  jengravinGS 


LEA   &   FEBIGER 
PHILADELPHIA  AND   NEW  YORK 


Copyright 
LEA  &  FEBIGER 
1918 


PRINTED  IN  U.  S.  A. 


THE  FIRST  EDITION    OF  THIS   WORK 
WAS    DEDICATED   TO 

SIR  BENJAMIN  COLLINS  BRODIE,  Bart.,  F.R.S.,  D.C.L. 

IN  ADMIRATION   OF 

HIS  GREAT  TALENTS 

AND    IN    REMEMBRANCE    OF 

MANY  ACTS  OF   KINDNESS   SHOWN    TO   THE    ORIGINAL 

AUTHOR  OF    THE   BOOK 

FROM  AN 

EARLY  PERIOD  OF  HIS  PROFESSIONAL  CAREER 


672.7 


PREFACE  TO  THE  TWENTIETH  EDITION. 


Since  the  publication  of  the  first  English  edition  of  this  work  in  1858  and  the 
first  American  edition  in  1859  great  advances  in  the  subject  of  Anatomy  have  been 
made,  especially  in  microscopic  anatomy  and  the  anatomy  of  the  embryo.  This 
knowledge  was  embodied  from  time  to  time  in  the  successive  editions  until  finally 
considerable  portions  of  the  text,  sometimes  sections,  were  devoted  to  these  sub- 
jects. Howe\'er,  the  main  text  has  always  remained  primarily  a  descriptive 
anatomy  of  the  human  body. 

In  the  present  edition  the  special  sections  on  embryology  and  histology  have 
been  distributed  among  the  subjects  under  which  they  naturally  belong.  New 
matter  on  physiological  anatomy,  laws  of  bone  architecture,  the  mechanics  and 
variations  of  muscles  have  been  added,  occupying  much  of  the  space  formerly 
devoted  to  the  sections  on  applied  anatomy. 

The  sections  on  the  ductless  glands  and  the  nervous  system  have  been  largely 
rewritten.  In  the  latter  a  more  rational  presentation  of  the  sympathetic  nervous 
system  has  been  achieved  through  the  use  of  diagrams  and  descriptions  based  on 
physiological  and  pharmacological  work.  The  central  connections  of  the  spinal 
and  cranial  nerves  are  also  emphasized. 

Illustrations  have  been  added  wherever  important  points  could  be  made  more 
clear,  and  throughout  the  work  colored  pictures  have  been  even  more  extensively 
used  than  heretofore.  In  this  respect  special  mention  might  be  made  of  the  central 
nervous  system  and  the  section  on  the  muscles.  In  the  section  on  Syndesmolog}" 
six  illustrations  are  used  from  Quain's  Anatomy  through  the  courtesy  of  the 
publishers,  Messrs.  Longmans,  Green  &  Company,  of  London. 

The  use  of  the  B.  N.  A.  nomenclature  in  English  has  been  retained  practically 
unchanged  in  this  edition  and  important  references  to  the  literature  have  been 
added  at  the  end  of  each  section. 

As  a  practical  work  on  the  subject  for  the  student,  Gray's  Anatomy  has  always 
been  recognized  and  appreciated.  The  plan  originally  formulated,  which  has 
proved  so  successful,  has  been  adhered  to  as  much  as  possible.  It  is  interesting  to 
note  that  although  Henry  Gray  saw  only  the  first  edition,  much  of  the  original 
text  persists  and  many  of  his  illustrations  are  still  in  use.  Bearing  this  in  mind  it 
has  been  the  endeavor  of  the  Editor  to  supply  only  such  changes  as  advances  in 
the  science  made  necessary  in  order  that  this  work  may  reflect  the  latest  accessions 
to  anatomical  knowledge. 

W.  H.  L. 

Baltimore,  1918. 


CONTENTS. 


EMBRYOLOGY. 


The  Animal  Cell. 


Cytoplasm 35 

Nucleus 36 

Reproduction  of  Cells 36 

Prophase 36 

Metaphase •      •  36 

Anaphase     ...  36 

Telophase    ...  .      .  38 

The  Ovum. 


The  Primitive  Segment       .  52 

Separation  of  the  Embryo     .  53 

The   Yolk-sac  ....        54 

Development  of  the  Fetal  Membranes  and  Placenta. 


Yolk  .  39 

Germinal  Vesicle 40  ]  The  Decidua 

Coverings  of  the  Ovum 40    The  Chorion 

Maturation  of  the  Ovum 40    The  Placenta 

Fetal  Portion 
The  Spermatozoon 


The  AUantois 

The  Amnion 

The  Umbilical  Cord  and  Body-stalk  . 
Implantation  or  Imbedding  of  the  Ovum 


Fertilization  of  the  Ovum 

Segmentation  of  the  Fertilized  Ovum. 

The    Primitive    Streak;    Formation    of    the 
Mesoderm 


Maternal  Portion   .... 
Separation  of  the  Placenta 

The  Branchial  Region. 
The  Branchial  or  Visceral  Arches  and  Pharyn- 


54 
56 
57 
58 
59 
60 
62 
62 
63 
64 


_     _  47  I      geal  Pouches 65 

Ectoderm" 47  |  The  Nose  and  Face 67 

Entoderm 49    The  Limbs 71 

Mesoderm 49  ^      ,  ,  ,     r.    7    ^     •.  •  to 

I  Development  of  the  Body  Cavities     .      .  7J 

The  Neural  Groove  and  Tube     .      .       50  ^.„  c. 

I    The  Form  of  the  Embryo  at  Different  Stages 

The  Notochord  ....        52  i  of  its  Growth         ....  74 


OSTEOLOGY. 


Long  Bones 79 

Short  Bones 79 

Flat  Bones 79 

Irregular  Bones 80 

Surfaces  of  Bones 80 

Development  of  the  Skeleton. 

The  Skeleton 80 

The  Vertebral  Column 80 

The  Ribs 82 

The  Sternum 83 

The  Skull 83 

Bone. 

"Structure  and  Physical  Properties       ...  86 

Periosteum           87 

Marrow 87 

Vessels  and  Nerves  of  Bone 88 

Minute  Anatomy 89 

Chemical  Composition         91 

Ossification    ..........  91 

Intramembranous  Ossification      ...  91 

Intercartilaginous  Ossification      ...  93 

The  Vertebral  Column. 
General  Characteristics  of  a  Vertebra. 


The  Cervical  Vertebrae 

The  First  Cervical  Vertebra  . 
The  Second  Cervical  Vertebra 
The  Seventh  Cervical  Vertebra 


97 

99 

100 

101 


The  Thoracic  Vertebra 

The  First  Thoracic  Vertebra 
The  Ninth  Thoracic  Vertebra 
The  Tenth  Thoracic  Vertebra 
The  Eleventh  Thoracic  Vertebra 
The  Twelfth  Thoracic  Vertebra 

The  Lumbar  Vertebrae 

The  Fifth  Lumbar  Vertebra  . 

The  Sacral  and  Coccygeal  Vertebrae 

The  Sacrum 

The  Coccyx 

Ossification  of  the  Vertebral  Column 


The  Vertebral  Column  as  a  Whole. 


Curves 
Surfaces   . 
Vertebral  Canal 


102 
104 
104 
104 
104 
104 
104 
106 
106 
106 
111 
111 


114 
114 
116 


The  Thorax. 

Boundaries 117 

The  Sternuni 119 

Manubrium 120 

Body 120 

Xiphoid  Process 121 

The  Ribs        .      . 123 

Common  Characteristics  of  the  Ribs      .  123 

Peculiar  Ribs 125 

First  Rib 125 

Second  Rib 125 

Tenth  Rib 126 

Eleventh  and  Twelfth  Ribs        .      .  126 

The  Costal  Cartilages 127 

(9) 


10 


CONTENTS 


The  Skull. 
The  Cranial  Bones. 

The  Occipital  Bone 129 

The  Squama 129 

Lateral  Parts 131 

Basilar  Parts 132 

Angles 132 

The  Parietal  Bone 133 

The  Frontal  Bone 135 

Squama 135 

Orbital  or  Horizontal  Part     ....  137 

The  Temporal  Bone 138 

The  Squama 139 

Mastoid  Portion 141 

Petrous  Portion 142 

Tympanic  Part 145 

Styloid  Process 145 

The  Sphenoid  Bone 147 

Body 147 

The  Great  Wings 149 

The  Small  AVings 151 

Pterygoid  Processes 151 

The  Sphenoidal  Conchae   .      .      .      .      .  152 

Ethmoid  bone 153 

Cribriform  plate 153 

Perpendicular  Plate 154 

Labyrinth  or  Lateral  Mass     ....  154 

Sutural  or  Wormian  Bones 156 


The  Facial  Bones. 

The  Nasal  Bones 156 

The  Maxillae  (Upper  Jaw) 157 

The  Maxillary  Sinus  or  Antrum  of  High- 
more 160 

The  Zygomatic  Process 161 

The  Frontal  Process 161 

The  Alveolar  Process 161 

The  Palatine  Process 162 

Changes  Produced  in  the  Maxilla  by  Age  163 

The  Lacrimal  Bone 163 

The  Zygomatic  Bone 164 

The  Palatine  Bone 166 

The  Horizontal  Part 167 

The  Vertical  Part 167 

The  Pyramidal  Process  or  Tuberosity    .  168 

The  Orbital  Process 168 

The  Sphenoidal  Process 169 

The  Inferior  Nasal  Concha 169 

The  Vomer 170 

The  Mandible  (Lower  Jaw)      .      .      .  '    .      .  172 
Changes  Produced  in  the  Mandible  by 

Age  175 

The  Hyoid  Bone       !!!!!!!!  177 


The  Exterior  of  the  Skull. 

Norma  Verticalis 178 

Norma  Basalis 179 

Norma  Lateralis 182 

The  Temporal  Fossa 183 

The  Infratemporal  Fossa        .  .      .184 

The  Pterygopalatine  Fossa    .      .      .      .185 

Norma  Occipitalis 185 

Norma  Frontalis 185 

The  Orbitf 188 


The  Interior  of  the  Skull. 

Inner  Surface  of  the  Skull-cap      .  .      .189 

Under  Surface  of  the  Base  of  the  Skull    .  190 

The  Anterior  Fossa 190 

The  Middle  Fossa        ......  190 

The  Posterior  Fossa 192 

The  Nasal  Cavity 194 

Anterior  Nasal  Aperture 196 

Differences  in  the  Skull  Due  to  Age   .  196 

Sexual  Differences  in  the  Skull      ....  197 

Craniology 197 


Thk  Extremities. 
The  Bones  of  the  Upper  Extremity. 


The 


The 


The 


The 


The 


Clavicle 

Lateral  Third     .... 

Medial  Two-thirds 

The  Sternal  Extremity 

The  Acromial  Extremity  . 

Scapula        .... 

The  Spine 

The  Acromion  .... 

The  Coracoid  Process 

Humerus 

Upper  Extremity    . 

The  Head         ... 
The  Anatomical  Neck 
The  Greater  Tubercle 
The  Lesser  Tubercle 
The  Body  or  Shaft     . 

The  Lower  Extremity 

Ulna 

The  Upper  Extremity 
The  Olecranon 
The  Coronoid  Process 
The  Semilunar  Notch 
The  Radial  Notch      . 

The  Body  or  Shaft       .      . 

The  Lower  Extremity 

Radius 

The  Upper  Extremity 

The  Body  or  Shaft       .      . 

The  Lower  Extremity 


20011 

200 

201 

202 

202 

202 

203 

203 

207 

209 

209 

209 

209 

209 

209 

209 

212 

214 

214 

214 

214 

215 

215 

215 

218 

219 

219 

219 

220 


The  Hand. 

The  Carpus 221 

Common  Characteristics  of  the  Carpal 

Bones       . 221 

Bones  of  the  Proximal  Row   ....  221 

The  Navicular  Bone        ....  221 

The  Lunate  Bone 224 

The  Triangular  Bone       ....  224 

The  Pisiform  Bone 225 

Bones  of  the  Distal  Row         ....  225 

The  Greater  Multangular  Bone  225 

The  Lesser  Multangular  Bone  .      .  225 

The  Capitate  Bone 226 

The  Hamate  Bone 227 

The  Metacarpus       .      . 227 

Common  Characteristics  of  the  Meta- 
carpal Bones 227 

Characteristics  of  the  Individual  Meta- 
carpal Bones 228 

The  First  Metacarpal  Bone       .      .  228 

The  Second  Metacarpal  Bone    .      .  228 

The  Third  Metacarpal  Bone      .      .  228 

The  Fourth  Metacarpal  Bone    .  228 

The  Fifth  Metacarpal  Bone       .      .  228 

The  Phalanges  of  the  Hand 230 

Ossification  of  the  Bones  of  the  Hand     .  230 

The  Bones  of  the  Lower  Extremity. 

The  Hip  Bone 231 

The  Ilium 231 

The  Body        .......  231 

The  Ala 232 

The  Ischium 234 

The  Body 234 

The  Superior  Ramus       ....  235 

The  Inferior  Ramus 235 

The  Pubis 236 

The  Body 236 

The  Superior  Ramus       ....  236 

The  Inferior  Ramus 237 

The  Acetabulum 237 

The  Obturator  Foramen       .      .  237 

The  Pelvis 238 

The  Greater  or  False  Pelvis  ....  238 

The  Lesser  or  True  Pelvis      ....  239 

Axes ...  240 

Position  of  the  Pelvis 241 

Differences  between  Male  and  Female 

Pelves 241 

Abnormalities 242 


CONTENTS 


The  Femur 

The  Upper  Extremity 

The  Head 

The  Neck 

The  Trochanters 

The  Body  or  Shaft 

The  Lower  Extremity 

The  Architecture  of  the  Femur    . 

The  Patella 

The  Tibia 

The  Upper  Extremity 

The  Body  or  Shaft 

The  Lower  Extremity 

The  Fibula 

The  Upper  Extremity  or  Head    . 

The  Body  or  Shaft 

The     Lower     Extremity     or     Lateral 
Malleolus 


The  Foot. 


The  Tarsus    . 

The  Calcaneus 


242 
243 
243 
243 
244 
246 
247 
248 
255 
256 
256 
257 
259 
260 
260 
260 

262 


263 
263 


The  Tarsus—  ^^^^_ 

The  Talus    ....      J^^^^     .  266 

The  Cuboid  Bone  .      .      .  ^^^^.      .  269 

The  Navicular  Bone 270 

The  First  Cuneiform  Bone     ....  270 

The  Second  Cuneiform  Bone        .      .      .  271 
The  Third  Cuneiform  Bone    .      .      .      .271 

The  Metatarsus 272 

Common  Characteristics  of  the   Meta- 
tarsal Bones        .      .      .      .      .      .      .  272 

Characteristics  of  the  Individual  Meta- 
tarsal Bones 272 

The  First  Metatarsal  Bone  .      .      .  272 

The  Second  Metatarsal  Bone     .      .  273 

The  Third  Metatarsal  Bone       .      .  274 

The  Fourth  Metatarsal  Bone     .      .  274 

The  Fifth  Metatarsal  Bone        .      .  274 

The  Phalanges  of  the  Foot 275 

Ossification  of  the  Bones  of  the  Foot        .      ■  275 
Comparison  of  the  Bones  of  the  Hand  and 

Foot 276 

The  Sesamoid  Bones 277 


SYNDESMOLOGY. 


Bone 279 

Hyahne  Cartilage 279 

Articular  Cartilage 280 

Costal  Cartilage      . 281 

White  Fibrocartilage 281 

Ihterarticular  Fibrocartilages        .       .      .  281 

Connecting  Fibrocartilages     ....  282 

Circumferential  Fibrocartilages    .      .      .  282 

Stratiform  Fibrocartilages       ....  282 

Ligaments 282 

The  Articular  Capsules 282 

Mucous  Sheaths 283 

Bursse  Mucosae 283 

Development  of  the  Joints    .      .  283 


Classification  of  Joints 

Synarthrosis 284 

Sutura 284 

Schindylesis 284 

Gomphosis 284 

Synchondrosis 284 

Amphiarthrosis 285 

Diathrosis 285 

Ginglimus 285 

Trochoid 285 

Condyloid    .      .      .  _    .      .      .      .   _  .      .286 

Articulation  by  Reciprocal  Reception    .  286 

Enarthrosis 286 

Arthrodia 286 


The  Kind  of  Movement  Admitted  in  Joints. 

Gliding  Movement 286 

Angular  Movement 286 

Circumduction 286 

Rotation 287 

Ligamentous  Action  of  Muscles    ....  287 

I^V  Articulations  of  the  Thunk. 

I H       Articulations  of  the  Vertebral  Column  287 

I^L  Articulations  of  Vertebral  Bodies  287 

I^H  The    Anterior    Longitudinal    Liga- 

l^t^  ment  .  ..287 

I^^^^K  The    Posterior    Longitudinal    Liga- 

|^^H|  ment 288 

l^^^^r  The  Intervertebral    Fibrocartilages  289 

I^V  Structure 289 

1^^  Articulations  of  Vertebral  Arches  289 

I^^^K  The  Articular  Capsules  ....  290 

I^^^B.  The  Ligamenta  Flava      ....  290 

1^^^^^^^^     The  Supraspinal  Ligament   .  290 


Articulations  of  the  Vertebral  Column — 
Articulations  of  Vertebral  Arches — 

The  Ligamentum  Nuchse      .      .      .  290 
The  Interspinal  Ligaments  .      .      .  291 
The  Intertransverse  Ligaments       .  291 
Articulation  of  the  Atlas  with  the  Epistro- 
pheus or  Axis 292 

The  Articular  Capsules 292 

The  Anterior  Atlantoaxial  Ligament      .  293 

The  Posterior  Atlantoaxial  Ligament     .  293 

The  Transverse  Ligament  of  the  Atlas  .  293 
Articulations  of  the  Vertebral  Column  with 

the  Cranium        .......  295 

Articulation    of    the    Atlas    with    the 

Occipital  Bone 295 

The  Articular  Capsules  ....  295 
The  Anterior  Atlantooccipital  Mem- 
brane        295 

The  Posterior  Atlantooccipital  Mem- 
brane        296 

The  Lateral  Ligaments   ....  296 
Ligaments  Connecting  the  Axis  with  the 

Occipital  Bone 296 

The  Membrana  Tectoria        .      .      .  296 

The  Alar  Ligaments 296 

Articulation  of  the  Mandible 297 

The  Articular  Capsule 297 

The  Temporomandibular  Ligament        .  297 

The  Sphenomandibular  Ligament     .      .  297 

The  Articular  Disk 298 

The  Stylomandibular  Ligament  .      .  298 

Costovertebral  Articulations 299 

Articulations  of  the  Heads  of  the  Ribs  .  299 
The  Articular  Capsule  ....  299 
The  Radiate  Ligament  ....  299 
The  Interarticular  Ligament  .  .  300 
Costotransverse  Articulations  .  .  300 
The  Articular  Capsule  ....  301 
The  Anterior  Costotransverse  Liga- 
ment         301 

The  Posterior  Costotransverse  Liga- 
ment         301 

The  Ligament  of  the  Neck  of  the 

Rib 302 

The  Ligament  of  the  Tubercle  of 

the  Rib 302 

Sternocostal  Articulations 302 

The  Articular  Capsules     .    _ .      .      .      .  302 
The  Radiate  Sternocostal  Ligaments     .  302 
The    Interarticular   Sternocostal    Liga- 
ment    303 

The  Costoxiphoid  Ligaments       .      .      .  304' 

Interchondral  Articulations    ....  304 

Costochondral  Articulations  ....  304 
Articulation  of  the  Manubrium  and  Body  of 

the  Sternum 304 

Mechanism  of  the  Thorax      ....  304 


12 


CONTENTS 


Articulation  of  the  Vertebral  Column  with 

the  Pelvis 306 

The  Iliolumbar  Ligament       ....  306 

Articulations  of  the  Pelvis 306 

Sacroiliac  Articulation 306 

The  Anterior  Sacroiliac  Ligament  .  307 
The  Posterior  Sacroiliac  Ligament.  307 
The    Interosseous   Sacroiliac    Liga- 
ment      . 308 

Ligaments  Connecting  the  Sacrum  and 

Ischium 309 

The  Sacrotuberous  Ligament           .  309 
The  Sacrospinous  Ligament       .      .  309 
Sacrococcygeal  Symphysis      ....  309 
The  Anterior  Sacrococcygeal  Liga- 
ment        •  .      .  309 

The  Posterior  Sacrococcygeal  Liga- 
ment         309 

The  Lateral  Sacrococcygeal   Liga- 
ment         310 

The  Interarticular  Ligaments    .      .  310 

The  Pubic  Symphysis 310 

The  Anterior  Pubic  Ligament     .      .  310 

The  Posterior  Pubic  Ligament  .      .  310 

The  Superior  Pubic  Ligament    .      .  310 

The  Arcuate  Pubic  Ligament    .  310 
The  Interpubic  Fribrocartilaginous 

Lamina 311 

Mechanism  of  the  Pelvis 311 


Articulations  of  the  Upper  Extremity. 

Sternoclavicular  Articulation 313 

The  Articular  Capsule 313 

The  Anterior  Sternoclavicular  Ligament  313 
The    Posterior    Sternoclavicular    Liga- 
ment    313 

The  Interclavicular  Ligament      .      .      .  314 
The  Costoclavicular  Ligament     .      .      .314 

The  Articular  Disk 314 

Acromioclavicular  Articulation      .  .  315 

The  Articular  Capsule 315 

The   Superior   Acromioclavicular   Liga- 
ment    315 

The    Inferior    Acromioclavicular    Liga- 
ment    315 

The  Articular  Disk 315 

The  Coracoclavicular  Ligament  .      .      .  315 
The  Trapezoid  Ligament        .      .      .      .315 

The  Conoid  Ligament 315 

The  Ligaments  of  the  Scapula  .      .  316 

The  Coracoacromial  Ligament    .      .      .  316 

The  Superior  Transverse  Ligament  .      .  317 

The  Inferior  Transverse  Ligament    .      .  317 

Humeral  Articulation  or  Shoulder-joint  .      .  317 

The  Articular  Capsule 317 

The  Coracohumeral  Ligament     .      .      .  318 

Glenohumeral  Ligaments        .      .      .      .  318 

The  Transverse  Humeral  Ligament        .  319 

The  Glenoidal  Labrum 319 

Bursae 319 

Elbow-joint 321 

The  Anterior  Ligament 321 

The  Posterior  Ligament 322 

The  Ulnar  Collateral  Ligament  .      .      .  322 

The  Radial  Collateral  Ligament        .      .  322 

Radioulnar  Articulation 324 

Proximal  Radioulnar  Artifculation    .      .  324 

The  Annular  Ligament   ....  324 

Middle  Radioulnar  Union       ....  325 

The  Oblique  Cord 325 

The  Interosseous  Membrane      .      .  325 

Distal  Radioulnar  Articulation    .      .      .  325 

The  Volar  Radioulnar  Ligament     .  325 

The  Dorsal  Radioulnar  Ligament  .  325 

The  Articular  Disk 325 

Radiocarpal  Articulation  or  Wrist-joint  .      .  327 

The  Volar  Radiocarpal  Ligament      .      .  327 

The  Dorsal  Radiocarpal  Ligament    .      .  328 

The  Ulnar  Collateral  Ligament  .  .  328 

The  Radial  Collateral  Ligament  .  328 

Intercarpal  Articulations 328 

Articulations  of  the  Proximal  Row  of 

Carpal  Bones 328 


Intercarpal  Articulations — 

Articulations  of  the  Proximal   Row  of 

Carpa   Bones — 

The  Dorsal  Ligaments    . 

The  Volar  Ligaments 

The  Interosseous  Ligaments 

Articulations    of    the    Distal    Row    of 

Carpal  Bones 

The  Dorsal  Ligaments    . 
The  Volar  Ligaments 
The  Interosseous  Ligaments 
Articulations    of    the     Two     Rows    of 
Carpal  Bones  with  Each  Other 
The  Volar  Ligaments 
The  Dorsal  Ligaments     . 
The  Collateral  Ligaments     . 
Carpometacarpal  Articulations 

Carpometacarpal    Articulation    of    the 

Thumb 

Articulations  of  the  Other  Four  Meta 
carpal  Bones  with  the  Carpus 
The  Dorsal  Ligaments    . 
The  Volar  Ligaments 
The  Interosseous  Ligaments 
Intermetacarpal  Articulations 

The  Transverse  Metacarpal  Ligament 
Metacarpophalangeal  Articulations    . 

The  Volar  Ligaments 

The  Collateral  Ligaments 
Articulations  of  the  Digits        .... 


328 
328 
328 

329 
329 
329 
329 

329 
329 
329 
329 
330 

330 

331 
331 
331 
331 
331 
331 
332 
332 
332 
333 


Articulations  of  the  Lower  Extremity. 


Coxal  Articulation  or  Hip-joint     . 

The  Articular  Capsule       .... 
The  Iliofemoral  Ligament 
The  Pubocapsular  Ligament 
The  Ischiocapsular  Ligament 
The  Ligamentum  Teres  Femoris 
The  Glenoidal  Labrum      .... 
The  Transverse  Acetabular  Ligament 

The  Knee-joint 

The  Articular  Capsule       .... 
The  Ligamentum  Patellae 
The  Oblique  Popliteal  Ligament 
'The  Tibial  Collateral  Ligament  . 
The  Fibular  Collateral  Ligament 
The  Cruciate  Ligaments  .... 

The  Anterior  Cruciate  Ligament 

The  Posterior  Cruciate  Ligament 
The  Menisci 

The  Medial  Meniscus 

The  Lateral  Meniscus 
The  Transverse  Ligament 
The  Coronarj'  Ligaments 

Bursae 

Articulations  between  the  Tibia  and 
Tibiofibular  Articulation 

The  Articular  Capsule     . 

The  Anterior  Ligament  . 

The  Posterior  Ligament 
Interosseous  Membrane    . 
Tibiofibular  Syndesmosis 

The  Anterior  Ligament  . 

The  Posterior  Ligament 

The  Inferior  Transverse  Ligament 

The  Interosseous  Ligament 
Talocrural  Articulation  or  Ankle-joint  . 
The  Articular  Capsule  .... 
The  Deltoid  Ligament  .... 
The  Anterior  Talofibular  Ligament 
The  Posterior  Talofibular  Ligament 
The  Calcaneofibular  Ligament    . 

Intertarsal  Articulations 

Talocalcaneal  Articulation 

The  Articular  Capsule     . 

The   Anterior   Talocalcaneal   Liga 
ment 

The  Posterior  Talocalcaneal  Liga 
ment 

The    Lateral    Talocalcaneal    Liga 
ment 

The    Medial    Talocalcaneal    Liga 
ment 


333 
334 
335 
335 
335 
336 
336 
336 
339 
340 
340 
340 
341 
341 
342 
342 
342 
342 
343 
343 
343 
343 
345 
347 
348 
348 
348 
348 
348 
348 
348 
348 
349 
349 
349 
350 
350 
351 
351 
351 
352 
352 
352 

352 

352 

352 

353 


CONTENTS 


13 


Intertarsal  Articulations — 

Talocalcaneal  Articulation — 

The   Interosseous   Talocalcaneal 

Ligament 

Talocalcaneonavicular  Articulation  . 
The  Articular  Capsule     . 
The  Dorsal  Talonavicular  Ligamen 
Calcaneocuboid  Articulation 
The  Articular  Capsule     . 
TheDorsalCalcaneocuboidLigament 
The  Bifurcated  Ligament 
The  Long  Plantar  Ligament 
The  Plantar  Calcaneocuboid  Liga 

ment 

The  Ligaments  Connecting  the  Calca 
neus  and  Navicular 
The   Plantar   Calcaneonavicular 

Ligament 

Cuneonavicular  Articulation 
The  Dorsal  Ligaments    . 
The  Plantar  Ligaments  . 
Cuboideonavicular  Articulation  . 
The  Dorsal  Ligament 


353 
353 
354 
354 
354 
354 
354 
354 
354 

354 

355 

355 
356 
356 
356 
356 
357 


Intertarsal  Articulations — 

Cuboideonavicular  Articulation — 

The  Plantar  Ligament    ....  357 
The  Interosseous  Ligament        .      .  357 
Intercuneiform  and  Cuneocuboid  Articu- 
lation        357 

The  Dorsal  Ligaments    ....  357 

The  Plantar  Ligaments  ....  357 

The  Interosseous  Ligaments      .      .  357 

Tarsometatarsal  Articulations       ....  358 

The  Dorsal  Ligaments 358 

The  Plantar  Ligaments 358 

The  Interosseous  Ligaments  ....  358 

Intermetatarsal  Articulations 358 

The  Dorsal  Ligaments 358 

The  Plantar  Ligaments 358 

The  Interosseous  Ligaments  ....  358 

The  Transverse  Metatarsal  Ligament    .  359 

Metatarsophalangeal  Articulations     .      .      .  359 

The  Plantar  Ligaments 359 

The  Collateral  Ligaments       ....  359 

Articulations  of  the  Digits 359 

Arches  of  the  Foot 360 


MYOLOGY. 


Mechanics  of  Muscle. 

The  Direction  of  Muscle  Pull         .      . 
The  Action  of  Muscle  Pull  on  Tendon 
The  Strength  of  Muscles     .... 
The  Work  Accomplished  by  Muscles 
The  Action  of  Muscles  on  Joints 


363 
364 
364 
365 
368 


Development  of  the  Muscles. 

The  Ventro-lateral  Muscles  of  the  Neck  .      .  371 

Muscles  of  the  Shoulder  Girdle  and  Arm       .  371 

The  Muscles  of  the  Leg 372 

The  Muscles  of  the  Head 372 

Striped  or  Voluntary  Muscle 373 

_  ^     Vessels  and  Nerves  of  Striped  Muscle      .      .  376 

■  H  Tendons,  Aponeuroses,  and  Fascia. 

■  H    Tendons 376 

■  H     Aponeuroses 376 

■  ■     Fasciaj 376 

I  ^^^^  The  Fascia  and  Muscles  of  the  Head. 

■  ^^HB  The  Muscles  of  the  Scalp. 

The  Skin  of  the  Scalp 378 

The  Superficial  Fascia 378 

Epicranius 378 

Occipitalis 379 

Frontalis 379 

Galea  Aponeurotica 380 

The  Muscles  of  the  Eyelid. 

Orbicularis  Oculi 380 

Corrugator 381 

The  Muscles  of  the  Nose. 

Procerus  ...  382 

Nasalis 382 

Depressor  Septi .      .  382 

Dilator  Naris  Posterior 382 

Dilator  Naris  Anterior 382 

The  Muscles  of  the  Mouth. 

Quadratus  Labii  SuperioriD 383 

Caninus 383 

Zygomaticus 383 

t: 


Quadratus  Labii  Inferioris 383 

Triangularis 383 

Buccinator 384 

Pterygomandibular  Raph6     ....  384 

Orbicularis  Oris 384 

Risorius 385 

The  Muscles  of  Mastication. 

Parotideomasseteric  Fascia 385 

Masseter 385 

Temporal  Fascia 386 

Temporalis 386 

Pterygoideus  Externus 386 

Pterygoideus  Internus 387 


The  Fascia  and  Muscles  of  the  Antero- 
lateral Region  of  the  Neck. 

The  Superficial  Cervical  Muscle. 

Superficial  Fascia 387 

Platysma 388 

Variations 388 

The  Lateral  Cervical  Muscles. 

The  Fascia  Colli  388 

Sternocleidomastoideus 390 

Variations 390 

Triangles  of  the  Neck 390 

The  Supra-  and  Infrahyoid  Muscles. 

Digastricus 391 

Variations 391 

Stylohyoideus 392 

Variations 392 

The  Stylohyoid  Ligament       ....  392 

Mylohyoideus 393 

Variations 393 

Geniohyoideus 393 

Sternohyoideus 393 

Variations 393 

Sternothyreoideus 393 

Variations 394 

Thyreohyoideus 394 

Omohyoideus 394 

Variations 394 

The  Anterior  Vertebral  Muscles. 

Longus  Colli 394 

Longus  Capitis 395 

Rectus  Capitis  Anterior 395 

Rectus  Capitis  Lateralis 395 


14 


CONTENTS 


The  Lateral   Vertebral  Muscles. 

Scalenus  Anterior 396 

Scalenus  Medius 396 

Scalenus  Posterior 396 

Variations 396 


The  Fasci.e  and  Muscles  of  the  Thunk. 

The  Deep  Muscles  of  the  Back. 

The  Lumbodorsal  Fascia 397 

Splenius  Capitis 397 

Splenius  Cervicis 397 

Variations 397 

Sacrospinalis 397 

Iliocostalis  Lumborum 399 

Iliocostalis  Dorsi 399 

Iliocostalis  Cervicis 399 

Longissimus  Dorsi 399 

Longissimus  Cervicis 399 

Longissimus  Capitis 399 

Spinalis  Dorsi 399 

Spinalis  Cervicis 400 

Spinalis  Capitis 400 

Semispinalis  Dorsi 400 

Semispinalis  Cervicis 400 

Semispinalis  Capitis 400 

Multifidus 400 

Rotatores 400 

Interspinales 400 

Extensor  Coccygis 401 

Intertransversarii 401 


The  Suboccipital  Muscles. 


Rectus  Capitis  Posterior  Major 
Rectus  Capitis  Posterior  Minor 
Obliquus  Capitis  Inferior    . 
Obliquus  Capitis  Superior  . 
The  Suboccipital  Triangle 


401 
401 
402 
402 
402 


The  Muscles  of  the  Thorax. 


Intercostal  Fascia 402 

Intercostales 403 

Intercostales  Externi 403 

Variations 403 

Intercostales  Interni 403 

Subcostales 403 

Transversus  Thoracis 403 

Levatores  Costarum 403 

Serratus  Posterior  Superior 404 

Variations 404 

Serratus  Posterior  Inferior 404 

Variations 404 

Diaphragm          404 

Medial  Lumbocostal  Arch      ....  404 

Lateral  Lumbocostal  Arch      ....  405 

The  Crura 405 

The  Central  Tendon 406 

Openings  in  the  Diaphragm         .      .      .  406 

Variations 406 

Mechanism  of  Respiration 407 

The  Muscles  and  Fascice  of  the  Abdomen. 

The  Antero-lateral  Muscles  of  the  Abdomen  408 

The  Superficial  Fascia 408 

Obliquus  Externus  Abdominis     .            .  409 
Aponeurosis      of       the       Obliquus 

Externus  Abdominis  .  .  410 
Subcutaneous  Inguinal  Ring  .  410 
The  Intercrural  Fibers  .  410 
The  Inguinal  Ligament  .  411 
The  Lacunar  Ligament  .  .  412 
The  Reflected  Inguinal  Liga- 
ment       412 

Ligament  of  Cooper                   .  412 

Variations 412 

Obliquus  Internus  Abdominis  412 

Variations 414 

Cremaster .      .  414 

Transversus  Abdominis                 ...  414 


The  Antero-lateral  Muscles  of  the  Abdomen — 
Transversus  Abdominis — 

Variations 414 

Inguinal  Aponeurotic  Falx   .      .      .  414 

Rectus  Abdominis 415 

Pyramidalis 416 

Variations 417 

The  Linea  Alba 417 

The  Lineae  Semilunares 417 

The  Transversalis  Fascia        ....  418 

The  Abdominal  Inguinal  Ring           .  418 

The  Inguinal  Canal 418 

Extraperitoneal  Connective  Tissue   .  418 

The  Deep  Crural  Arch 419 

The  Posterior  Muscles  of  the  Abdomen  .  419 
The    Fascia    Covering    the    Quadratus 

Lumborum 419 

Quadratus  Lumborum 420 

Variations 420 

The  Muscles  and  Fascice  of  the  Pelvis. 

Pelvic  Fascia 420 

Levator  Ani 422 

Coccygeus 424 

The  Muscles  and  Fascice'  of  the  Perineum. 

Muscles  of  the  Anal  Region 424 

The  Superficial  Fascia 424 

The  Deep  Fascia 425 

Ischiorectal  Fossa 425 

The  Corrugator  Cutis  Ani      ....  425 

Sphincter  Ani  Externus 425 

Sphincter  Ani  Internus                  .      .  426 

The   Muscles  of   the   Urogenital   Region  in 

the  Male 426 

Superficial  Fascia 426 

The    Central    Tendinous    Point    of    the 

Perineum 427 

Transversus  Perinsei  Superficialis      .      .  427 

Variations 427 

Bulbocavernosus 428 

Ischiocavernosus 428 

The  Deep  Fascia 428 

Transversus  Perinsei  Profundus         .      .  429 

Sphincter  Urethrae  Membranacese    .      .  429 

The  Muscles  of  the  Urogenital  Region  in  the 

Female 430 

Transversus  Perinsei  Superficialis      .      .  43o 

Bulbocavernosus 43Q 

Ischiocavernosus 430 

Transversus  Perincei  Profundus               .  431 


The  Fascia  and  Muscles  of  the  Upper 
Extremity. 

The  Muscles  Connecting  the  Upper  Extremity 
to  the  Vertebral  Column. 

Superficial  Fascia 432 

Deep  Fascia .  432 

Trapezius 432 

Variations 432 

Latissimus  Dorsi 432 

Variations 434 

Rhomboideus  Major 434 

Rhomboideus  Minor 434 

Variations 435 

Levator  scapulae 435 

Variations 435 

The  Muscles  Connecting  the  Upper  Extremity  to 
the  Anterior  and  Lateral  Thoracic  Walls. 

Superficial  Fascia 435 

Pectoralis  Major 436 

Variations 437 

Coracoclavicular  Fascia 437 

Pectoralis  Minor 438 

Variations 438 

Subclavius 438 

Variations 438 

Serratus  Anterior 438 

Variations 439- 


CONTENTS 


15 


The  Muscles  and  Fascice  of  the  Shoulder. 

Deep  Fascia 439 

Deltoideus 439 

Variations 440 

Subscapular  Fascia 440 

Subscapularis '    .  440 

Supraspinatous  Fascia 440 

Supraspinatus     . 440 

Infraspinatous  Fascia 441 

Infraspinatus 441 

Teres  Minor 441 

Variations 442 

Teres  Major 442 

The  Muscles  and  Fasciae  of  the  Arm. 

Brachial  Fascia 442 

Coracobrachialis 443 

Variations 443 

Biceps  Brachii    . 443 

Variations 444 

Brachialis 444 

Variations^ 444 

Triceps  Brachii 444 

Variations 445 

The  Muscles  and  Fascia  of  the  Forearm. 

Antibrachial  Fascia 445 

The  Volar  Antibrachial  Muscles    ....  445 

The  Superficial  Group       .      .      .      .      .  446 

Pronator  Teres 446 

Variations 446 

Flexor  Carpi  Radialis      ....  446 

Variations 446 

Palmaris  Longus 446 

Variations 446 

Flexor  Carpi  Ulnaris        ....  447 

Variations 447 

Flexor  Digitorum  Sublimis  .  448 

Variations 448 

The  Deep  Group 448 

Flexor  Digitorum  Profundus            .  448 
Fibrous     Sheaths     of     the     Flexor 

Tendons 448 

Variations 449 

Flexor  Pollicis  Longus     ....  449 

Variations 449 

Pronator  Quadratus 449 

Variations 450 

The  Dorsal  Antibrachial  Muscles.  .451 

The  Superficial  Group 451 

Brachioradialis 451 

Variations 451 

Extensor  Carpi  Radialis  Longus  452 

Extensor  Carpi  Radialis  Brevis       .  452 

Variations       .      .      .      .      .      .  452 

Extensor  Digitorum  Communis       .  452 

Variations 454 

Extensor  Digiti  Quinti  Proprius      .  454 

Variations 454 

Extensor  Carpi  Ulnaris  ....  454 

Variations 454 

Anconseus 454 

The  Deep  Group 454 

Supinator 454 

Abductor  Pollicis  Longus  455 

Variations 455 

Extensor  Pollicis  Brevis        .      .      .  455 

Variations 455 

Extensor  Pollicis  Longus       .      .      .  455 

Extensor  Indicis  Proprius                 .  456 

Variations 456 

The  Muscles  and  Fascia;  of  the  Hand. 

Volar  Carpal  Ligament 456 

Transverse  Carpal  Ligament 456 

The  Mucous  Sheaths  of  the  Tendons  on  the 

Front  of  the  Wrist 457 

Dorsal  Carpal  Ligament 458 

The  Mucous  Sheaths  of  the  Tendons  on  the 

Back  of  the  Wrist      .             459 

Palmar  Aponeurosis 460 


Superficial     Transverse      Ligament     of     the 

Fingers 461 

The  Lateral  Volar  Muscles 461 

Abductor  Pollicis  Brevis 461 

Opponens  Pollicis 461 

Flexor  Pollicis  Brevis 461 

Adductor  Pollicis  (Obliquus)        ...  462 

Adductor  Pollicis  (Transversus)  462 

Variations 462 

The  Medial  Volar  Muscles 462 

Palmaris  Brevis 463 

Abductor  Digiti  Quinti 463 

Flexor  Digiti  Quinti  Brevis    ....  464 

Opponens  Digiti  Quinti 464 

Variations         464 

The  Intermediate  Muscles 464 

Lumbricales 464 

Variations 464 

Interossei 464 

Interossei  Dorsales 464 

Interossei  Volares 465 


The  Muscles  and  Fasci.*;  of  the  Lower 
Extremity. 

The  Muscles  and  Fascice  of  the  Iliac  Region. 

The  Fascia  Covering  the  Psoas  and  Iliacus  466 

Psoas  Major 467 

Psoas  Minor 467 

Iliacus 467 

Variations 467 

The  Muscles  and  Fascice  of  the  Thigh. 

The  Anterior  Femoral  Muscles     ....  467 

Superficial  Fascia 468 

Deep  Fascia 468 

The  Fossa  Ovalis 469 

Sartorius 470 

Variations 470 

Quadriceps  Femoris 470 

Rectus  Femoris 470 

Vastus  Lateralis 470 

Vastus  Medialis 471 

Vastus  Intermedius 471 

Articularis  Genu 471 

The  Medial  Femoral  Muscles        ....  471 

Gracilis 471 

Pectineus 472 

Adductor  Longus 472 

Adductor  Brevis 473 

Adductor  Magnus 473 

Variations 474 

The  Muscles  of  the  Gluteal  Region    .      .      .  474 

Gluteus  Maximus 474 

Bursae 474 

Glutaeus  Medius 474 

Variations 475 

Glutseus  Minimus 475 

Variations 475 

Piriformis 476 

Variations         476 

Tensor  Fasciae  Latae 476 

Obturator  Membrane 477 

Obturator  Internus 477 

Gemelli 477 

Gemellus  Superior 477 

Gemellus  Inferior 477 

Quadratus  Femoris 477 

Obturator  Externus 477 

The  Posterior  Femoral  Muscles     ....  478 

Biceps  Femoris 478 

Variations 479 

Semitendinosus 479 

Semimembranosus        ....  .  479 

Variations        ....  479 

The  Muscles  and  Fascice  of  the  Leg. 

The  Anterior  Crural  Muscles 480 

Deep  Fascia 480 

Tibialis  Anterior 480 

Variations 480 


16 


CONTENTS 


The  Anterior  Crural  Muscles — 

Extensor  Hallucis  Longus       .      .      .      .481' 

Variations 481 

Extensor  Digitorum  Longus  ....  481 

Variations 482 

PeroniEus  Tertius         482 

The  Posterior  Crural  Muscles        ....  482 

The  Superficial  Group 482 

Gastrocnemius      .....  482 

Variations 483 

Soleus 483 

Variations 483 

Tendo  Calcaneus 483 

Plantaris 483 

The  Deep  Group 483 

Deep  Transverse  Fascia        .      .      .  483 

Popliteus 484 

Variations 485 

Flexor  Hallucis  Longus  ....  485 

Variations 485 

Flexor  Digitorum  Longus     .      .      .  485 

Variations 485 

Tibialis  Posterior 485 

The  Lateral  Crural  Muscles 486 

Peronseus  Longus         486 

Peronseus  Brevis 486 

Variations        487 

The  Fascia  Around  the  Ankle. 

Transverse  Crural  Ligament 488 

Cruciate  Crural  Ligament 488 

Laciniate  Ligament ,  489 

Peroneal  Retinacula 489 


The  Mucous  Sheaths  of  the  Tendons  Around 
the  Ankle 

The  Muscles  and  Fasciae  of  the  Foot. 


I 


489 


The  Dorsal  Muscle  of  the  Foot     ....  490 

Extensor  Digitorum  Brevis    ....  490 

Variations 490 

The  Plantar  Muscles  of  the  Foot        .      .      .  490 

Plantar  Aponeurosis 490 

The  First  Layer 491 

Abductor  Hallucis 491 

Variations 491 

Flexor  Digitorum  Brevis       .      .      .491 

Variations 492 

Fibrous  Sheaths  of  the  Flexor 

Tendons 492 

Abductor  Digiti  Quinti   ....  492 

Variations 492 

The  Second  Layer 493 

Quadratus  Plantse 493 

Variations 493 

Lumbricales 493 

Variations 493 

The  Third  Layer 493 

Flexor  Hallucis  Brevis     ....  493 

Variations 493 

Adductor  Hallucis 493 

Variations 494 

Flexor  Digiti  Quinti  Brevis        .      .  494 

The  Fourth  Layer 495 

Interossei 495 

Interossei  Dorsales  ....  495 

Interossei  Plantares       .      .      .  495 


ANGIOLOGY. 


Structure  of  Arteries 498 

Capillaries 499 

Sinusoids 501 

Structure  of  Veins 591 


The  Blood. 

General  Composition  of  the  Blood      .            .  503 

Blood  Corpuscles 503 

Colored  or  Red  Corpuscles   .      .      .  503 

Colorless  Corpuscles  or  Leukocytes  504 


Development  of  the  Vascular  System. 

Further  Development  of  the  Heart     .      .      .  508 

The  Valves  of  the  Heart 514 

Further  Development  of  the  Arteries        .  515 

The  Anterior  Ventral  Aortae         .      .      .  516 

The  Aortic  Arches 516 

The  Dorsal  Aortse 517 

Further  Development  of  the  Veins      .      .      .  518 

The  Visceral  Veins 518 

The  Parietal  Veins 520 

Inferior  Vena  Cava 520 

Venous  Sinuses  of  the  Dura  Mater   .      .  522 


The  Thoracic  Cavity. 

The  Cavity  of  the  Thorax 524 

The  Upper  Opening  of  the  Thorax     .      .      .  524 

The  Lower  Opening  of  the  Thorax     .  524 

The  Pericardium. 

Structure  of  the  Pericardium 525 

The  Heart. 

Size 526 

Component  Parts 526 

Right  Atrium 628 

Sinus  Venarum 628 

Auricula 628 

Right  Ventricle 631 

Left  Atrium 633 

Auricula 533 

Left  Ventricle 635 

Ventricular  Septum 535 

Structure  of  the  Heart        ......  535 

The  Cardiac  Cycle  and  the  Actions  of  the 

Valves 538 

Peculiarities  in  the  Vascular  System  in  the 
Fetus. 

Fetal  Circulation 540 

Changes  in  the  Vascular  System  at  Birth     .  542 


THE  ARTERIES. 


The  Pulmonar 
Relations 

yA 

rtery 

.     543 
.     545 

The 

Aorta. 

The 

Ascending  Aorta. 

Relations 

.     546 

Branches 

.     646 

Branches  of  the  Ascending  Aorta — 

The  Coronary  Arteries 546 

Right  Coronary  Artery  ....  546 

Left  Coronary  Artery      ....  547 

Peculiarities 547 

The  Arch  of  the  Aorta. 

Relations 547 

Peculiarities         548 


CONTENTS 


17 


Branches 548 

Peculiarities 548 

The  Innominate  Artery 548 

Relations 548 

Branches 549 

Thyreoidea  Ima 549 

Collateral  Circxilation 549 


The  Arteries  of  the  Head  and  Neck. 


The  Common  Carotid  Artery. 

Relations 549 

Peculiarities 551 

Collateral  Circulation 551 

The  External  Carotid  Artery 551 

Relations 552 

Branches 552 

Superior  Thyroid  Artery       .      .      .  552 

Relations 552 

Branches 552 

Lingual  Artery 553 

Relations 553 

Branches 553 

External  Maxillary  Artery   .      .  553 

Relations 554 

Branches 554 

Peculiarities 556 

Occipital  Artery 556 

Course  and  Relations    .  556 

Branches 556 

Posterior  Auricular  Artery   .  557 

Branches 557 

Ascending  Pharj-ngeal  Artery    .      .  557 

Branches 558 

Superficial  Temporal  Artery  558 

Relations 558 

Branches 558 

Internal  Maxillary  Artery    .  559 

Branches 560 

The  Triangles  of  the  Neck 562 

Anterior  Triangle 563 

Inferior  Carotid  or   Muscular  Tri- 
angle         563 

Superior   Carotid    or   Carotid   Tri- 
angle         564 

Submaxillary     or     Digastric     Tri- 
angle         564 

Suprahyoid  Triangle        ....  565 

Posterior  Triangle 565 

Occipital  Triangle 565 

Subclavian  Triangle 565 

The  Internal  Carotid  Artery 566 

Course  and  Relations 567 

Cervical  Portion 567 

Petrous  Portion 567 

Cavernous  Portion 567 

Cerebral  Portion 567 

Peculiarities 567 

Branches  _ 568 

Caroticotympanic 568 

Artery  of  the  Pterygoid  Canal  .  568 

Cavernous 568 

Hypophyseal 568 

Semilunar 568 

Anterior  Meningeal 568 

Ophthalmic  artery 568 

Branches 568 

Anterior  Cerebral  Artery      .      .  571 

Branches 571 

Middle  Cerebral  Artery        .      .  572 

Branches 573 

Posterior  Communicating  Artery    .  573 

Anterior  Choroidal  Artery    .  .  574 


The  Arteries  of  the  Brain. 


The  Ganglionic  System 
The  Cortical  Arterial  System 
2 


575 
575 


The  Arteries  of  the  Upper  Extremity. 

The  Subclavian  Artery, 

First  Part  of  the  Right  Subcla\'ian  Artery    .  576 

Relations 576 

First  Part  of  the  Left  Subclavian  Artery       .  577 

Relations 577 

Second  and  Third  Parts  of  the  Subclavian 

Artery 577 

Relations 577 

Relations 577 

Peculiarities 577 

Collateral  Circulation 578 

Branches 578 

Vertebral  Artery 578 

Relations 578 

Branches   ........  579 

Thyrocer\acal  Trunk  .                  .      .      .  581 

Branches 581 

Peculiarities 583 

Internal  Mammarj'  Artery     ....  584 

Relations 584 

Branches 584 

The  Costocervical  Trunk        ....  585 

The  Axilla. 

Boundaries 585 

Contents 686 

The  Axillary  Artery 586 

Relations 586 

Collateral  Circulation 587 

Branches 587 

The  Highest  Thoracic  Artery    .  587 

The  Thoracoacromial  Artery     .  588 

The  Lateral  Thoracic  Artery     .  588 

The  Subscapular  Artery  .  .  .  588 
The  Posterior  Humeral  Circumflex 

Artery 589 

The  Anterior  Humeral  Circumflex 

Artery 589 

Peculiarities 589 

The  Brachial  Artery 589 

Relations 589 

The  Anticubital  Fossa 589 

Peculiarities 690 

Collateral  Circulation 690 

Branches 690 

The  Arteria  Profunda  Brachii  .  591 
The  Nutrient  Artery  .  .  .  .591 
The     Superior     Ulnar     Collateral 

Artery 591 

The   Inferior  Ulnar  Collateral 

Artery 592 

Muscular  Branches 592 

The  Anastomosis  Around  the  Elbow-joint  592 

The  Radial  Artery 592 

Relations 592 

Peculiarities 594 

Branches 594 

Radial  Recurrent  Artery      .      .      .  594 

Muscular 594 

Volar  Carpal 594 

Superficial  Volar 594 

Dorsal  Carpal       .      .      .      .      .  694 

Arteria  Princeps  PoUicis       .      .      .  595 

Arteria  Volaris  Indicis  Radialis       .  595 

Deep  Volar  Arch 595 

Volar  Metacarpal  Arteries    .  696 

Perforating 595 

Recurrent 596 

The  Ulnar  Artery 595 

Relations 595 

Peculiarities 596 

Branches 696 

Anterior  Ulnar  Recurrent  Artery    .  596 

Posterior  Ulnar  Recurrent  Artery  .  596 

Common  Interosseous  Artery    .      .  596 

Muscular 598 

Volar  Carpal 698 

Dorsal  Carpal 698 

Deep  Volar 598 

Superficial  Volar 598 

Relations 598 


18 


CONTENTS 


The  Arteries  of  the  Trunk. 

The  Descending  Aorta. 

The  Thoracic  Aorta 598 

Relations 599 

Peculiarities 599 

Branches 600 

Pericardial 600 

Bronchial 600 

Esophageal 600 

Mediastinal 600 

Intercostal  Arteries 600 

Branches        ...  .  601 

Subcostal  Arteries 601 

Superior  Phrenic 601 

The  Abdominal  Aorta 602 

Relations 603 

Collateral  Circulation 603 

Branches 603 

The  Celiac  Artery 603 

Relations 603 

The  Superior  Mesenteric  Artery      .  606 

Branches 607 

The  Inferior  Mesenteric  Artery       .  609 

Branches 610 

The  Middle  Suprarenal  Arteries      .  610 

The  Renal  Arteries 610 

The  Internal  Spermatic  Arteries     .  611 
The  Ovarian  Arteries      .      .      .      .611 

The  Inferior  Phrenic  Arteries    .      .  612 

The  Lumbar  Arteries      ....  612 

The  Middle  Sacral  Artery    ...  613 


The  Cominon  Iliac  Arteries. 

Peculiarities 614 

Collateral  Circulation 614 

The  Hypogastric  Artery 614 

Relations 614 

Peculiarities 615 

Collateral  Circulation 615 

Branches 615 

Superior  Vesical  Arterj'  .      .      .      .615 

Middle  Vesical  Artery     ....  615 

Inferior  Vesical  Artery    ....  615 

Middle  Hemorrhoidal  Artery     .      .  615 

Uterine  Artery 615 

Vaginal  Artery 616 

Obturator  Artery 616 

Branches 616 

Peculiarities  ......  617 

Internal  Pudendal  Artery-     .      .      .  617 

Relations 618 

Peculiarities 618 

Branches 618 

Inferior  Gluteal  Arterj-   ....  620 

Branches 620 

Lateral  Sacral  Arteries    .      .      .      .621 

Superior  Gluteal  Artery        .      .      .  622 

The  External  Iliac  Artery 622 

Relations 622 

Collateral  Circulation 622 

Branches 622 

Inferior  Epigastric  Artery    .      .      .  623 

Branches 623 

Peculiarities 623 

Deep  Iliac  Circumflex  Artery     .      .  623 


The  Arteries  of  the  Lower  Extremity. 

The  Femoral  Artery. 

The  Femoral  Sheath 6251 

The  Femoral  Triangle 628i 

The  Adductor  Canal 627 

Relations  of  the  Femoral  Artery  ....  627 

Peculiarities  of  the  Femoral  Artery     .       .       .  629 

Collateral  Circulation 629 

Branches 629 

Superficial  Epigastric  Artery  .  629 

Superficial  Iliac  Circumflex  Artery   .      .  629 

Superficial  External  Pudendal  Artery     .  629 

Deep  External  Pudendal  Artery  .  629 

Muscular     . 629 

Profunda  Femoris  Artery        ....  629 

Relations 630 

Peculiarities 630jb!^^ 

Branches    . 63(«l|^| 

Highest  Genicular  Artery        ....  631^fff3B 

The  Popliteal  Fo.ssa 031 

Boundaries 631 

Contents 632 

The  Popliteal  Artery 632 

Relations 632 

Peculiarities       .......  633 

Branches 633 

Superior  Muscular 633 

Sural  Arteries 633 

Cutaneous  Branches  ....  633 
Superior  Genicular  Arteries  .  633 
Middle  Genicular  Artery  .  033 
Inferior  Genicular  Arteries  .  .  633 
The  Anastomosis  Around  the  Knee- 
joint    .       .  634 

The  Anterior  Tibial  Artery 634 

Relations 635 

Peculiarities 635 

Branches 635 

Posterior  Tibial  Recurrent  Artery  .  635 

Fibular  Artery 635 

Anterior  Tibial  Recurrent  Arterj-   .  635 

Muscular  Branches 635 

Anterior  Medial  Malleolar  Artery  .  035 

Anterior  Lateral  Malleolar  Arterv  .  635 

The  Arteria  Dorsalis  Pedis       .      .      .      .  "    .  636 

Relations 636 

Peculiarities 636 

Branches 637 

Lateral  Tarsal  Artery      ....  637 

Medial  Tarsal  Artery      ....  637 

Arcuate  Artery 637 

Deep  Plantar  Arterj-        ....  637 

The  Posterior  Tibial  Artery 637 

Relations 637 

Peculiarities 638 

Branches 638 

Peroneal  Artery 638 

Peculiarities^ 638 

Branches 638 

Nutrient  Artery 638 

Muscular  Branches 639 

Posterior  Medial  Malleolar  Artery  639 

Communicating  Branch  ....  639 

Medial  Calcaneal 639 

Medial  Plantar  Artery     ....  039 

Lateral  Plantar  Arterj     ....  639 

Branches 640 


The  Pulmonary  Veins 
The  Systemic  Veins. 


THE  VEINS. 

.     642 


The  Veins  of  the  Heart. 

Coronary  Sinus 642 

Tributaries 642 

The  Veins  of  the  Head  and  Neck. 

The  Veins  of  the  Exterior  of  the  Head  and 

Face 644 

The  Frontal  Vein 644 


The  Veins  of  the  Exterior  of  the  Head 

and 

Face — 

The  Supraorbital  Vein 645 

The  Angular  Vein 

645 

The  Anterior  Facial  Vein 

645 

Tributaries      .... 

645 

The  Superficial  Temporal  Vein 

645 

Tributaries      .... 

645 

The  Pterygoid  Plexus 

645 

The  Internal  Maxillary  Vein . 

646 

The  Posterior  Facial  Vein 

646 

The  Posterior  Auricular  Vein 

646 

The  Occipital  Vein 

646 

CONTENTS 


19 


The  Veins  of  the  Neck 

The  External  Jugular  Vein 

Tributaries 
The  Posterior  External  Jugular  Vein 
The  Anterior  Jugular  Vein 
The  Internal  Jugular  Vein 

Tributaries 
The  Vertebral  Vein 

Tributaries 
The  Diploic  Veins    . 
The  Veins  of  the  Brain 
The  Cerebral  Veins 
The  External  Veins 

The  Superior  Cerebral  Vein 

The  Middle  Cerebral  Vein    . 

The  Inferior  Cerebral  Vein  . 

The  Internal  Cerebral  Veins 

The  Great  Cerebral  Vein 
The  Cerebellar  Veins  .... 
The  Sinuses  of  the  Dura  Mater.    Ophthalmic 
Veins  and  Emissary  Veins 
The  Superior  Sagittal  Sinus   . 
The  Inferior  Sagittal  Sinus     . 
The  Straight  Sinus       .... 
The  Transverse  Sinuses 
The  Occipital  Sinus     .... 
The  Confluence  of  the  Sinuses 
The  Cavernous  Sinuses 
The  Ophthalmic  Veins 

The  Superior  Ophthalmic  Vein 

The  Inferior  Ophthalmic  Vein 
The  Intercavernous  Sinuses 
The  Superior  Petrosal  Sinus 
The  Inferior  Petrosal  Sinus 
The  Basilar  Plexus 
The  Emissary  Veins 


The 


The 


The 


The  Veins  of  the   Upper  Extremity  and 
Thorax. 


Superficial  Veins  of  the  Upper  Extremity 

Digital  Veins 

The  Cephalic  Vein       .... 

The  Accessory  Cephalic  Vein 
The  Basilic  Vein     .... 
The  Median  Antibrachial  Vein 
Deep  Veins  of  the  Upper  Extremity 
Deep  Veins  of  the  Hand  . 
Deep  Veins  of  the  Forearm 
The  Brachial  Veins 
The  Axillary  Vein 
The  Subclavian  Vein 

Tributaries 
Veins  of  the  Thorax 
The  Innominate  Veins 

The  Right  Innominate  Vein 

The  Left  Innominate  Vein 

Tributaries      .... 

Peculiarities 
The  Internal  Mammary  Veins 
The  Inferior  Thyroid  Veins    . 
The  Highest  Intercostal  Vein 
The  Superior  Vena  Cava 

Relations 

The  Azygos  Vein    .... 

Tributaries      .... 
The  Hemiazygos  Veins 


646 
646 
647 
647 
647 
648 
648 
649 
650 
651 
652 
652 
652 
652 
652 
652 
653 
653 
653 

654 
654 
655 
655 
657 
658 
658 
658 
658 
659 
659 
659 
659 
659 
660 
660 


660 
660 
661 
662 
662 
662 
663 
663 
663 
663 
663 
664 
664 
664 
664 
664 
666 
666 
666 
666 
666 
666 
666 
667 
667 
667 
667 


The  Veins  of  the  Thorax — 
The  Azygos  Vein — 

The  Accessory   Hemiazygos 

Veins 667 

The  Bronchial  Veins 667 

The  Veins  of  the  Vertebral  Column    .      .      .  667 

The  External  Vertebral  Venous  Plexuses  668 

The  Internal  Vertebral  Venous  Plexuses  668 

The  Basivertebral  Veins 668 

The  Intervertebral  Veins         ...  669 

Th«  Veins  of  the  Medulla  Spinalis    .  669 

The  Veins  of  the  Lower  Extremity,  Abdomen, 
and  Pelvis. 

The  Superficial  Veins  of  the  Lower  Extremity  669 

The  Dorsal  Digital  Veins 669 

The  Great  Saphenous  Vein     ....  669 

Tributaries 670 

The  Small  Saphenous  Vein      ....  670 

The  Deep  Veins  of  the  Lower  Extremity       .  671 

The  Plantar  Digital  Veins      ....  671 

The  Posterior  Tibial  Veins     ....  672 

The  Anterior  Tibial  Veins      ....  672 

The  Popliteal  Vein 672 

The  Femoral  Vein 672 

The  Deep  Femoral  Vein  672 

The  Veins  of  the  Abdomen  and  Pelvis  .  672 

The  External  Iliac  Vein 672 

Tributaries 672 

The  Hypogastric  Veins 673 

Tributaries 673 

The  Hemorrhoidal  Plexus       ....  676- 

The  Pudendal  Plexus 676 

The  Vesical  Plexus 676. 

The  Dorsal  Veins  of  the  Penis     .      .      .  676 

The  Uterine  Plexuses 676 

The  Vaginal  Plexuses 677 

The  Common  Iliac  Veins        ....  677 

The  Middle  Sacral  Veins      ...  677 

Peculiarities 677 

The  Inferior  Vena  Cava 677 

Relations 678 

Peculiarities 678 

Applied  Anatomy 678 

Tributaries 678 

Lumbar  Veins 678 

Spermatic  Veins       ....  678 

Ovarian  Veins 679 

Renal  Veins 679 

Suprarenal  Veins      ....  679 

Inferior  Phrenic  Veins  .      .      .  679 

Hepatic  Veins 680 

The  Portal  System  of  Veins. 

The  Portal  Vein 681 

Tributaries 681 

The  Lienal  Vein 681 

Tributaries 681 

The  Superior  Mesenteric  Vein   .      .  682 

Tributaries 682 

The  Coronary  Vein 682 

The  Pyloric  Vein 682 

The  Cystic  Vein 682 

The  Parumbilical  Veins  ....  682 


THE  LYMPHATIC  SYSTEM. 


The  Development  of  the  Lymphatic  Vessels 
Lymphatic  Capillaries 

Distribution 

Lymphatic  Vessels 

Structure  of  Lymphatic  Vessels     .      .      .      . 
The  Lymph  Glands 

Structure  of  Lymph  Glands  .      .      .      . 

Hemolymph  Nodes         

Lymph 


The  Thoracic  Duct. 


The  Cistema  Chyli        .      . 

Tributaries 
The  Right  Lymphatic  Duct 

Tributaries 


683 
684 
684 
687 
687 
688 
688 
690 
690 


691 
691 
691 
692 


The  Lymphatics  of  the  Head,  Face, 
Neck. 

The  Lymph  Glands  of  the  Head   . 
The  Occipital  Glands  . 
The  Posterior  Auricular  Glands 
The  Anterior  Auricular  Glands 
The  Parotid  Glands     .      .      . 
The  Facial  Glands 
The  Deep  Facial  Glands  . 
The  Lingual  Glands 
The  Retropharyngeal  Glands 
The  Lymphatic  Vessels  of  the  Scalp 
The  Lymphatic  Vessels  of  the  Auricul 

and  External  Acoustic  Meatus 
The  Lymphatic  Vessels  of  the  Face 


692 
692 
693 
693 
693 
694 
694 
694 
694 
694 

694 
695 


20 


CONTENTS 


The  Lymph  Glands  of  the  Head— 

The   Lymphatic   Vessels   of   the    Nasal 

Cavities 695 

The  Lymphatic  Vessels  of  the  Mouth  .  695 
The  Lymphatic  Vessels  of  the  Palatine 

Tonsil 695 

The  Lymphatic  Vessels  of  the  Tongue  696 

The  Lymph  Glands  of  the  Neck  ....  697 

The  Submaxillary  Glands       ....  697 

The  Submental  or  Suprahyoid  Glands  .  697 

The  Superficial  Cervical  Glands  .      .    ' .  697 

The  Anterior  Cervical  Glands  .  .  697 
The  Deep  Cervical  Glands  .  .  .  .697 
The  Lymphatic  Vessels  of  the  Skin  and 

Muscles  of  the  Neck 698 


The  Lymphatics  of  the  Upper  Extremity. 

The  Lymph  Glands  of  the  Upper  Extremity  699 

The  Superficial  Lymph  Glands    .      .      .  699 

The  Deep  Lymph  Glands       ....  699 

The  Axillary  Glands        ....  699 

The     Lymphatic     Vessels     of     the     Upper 

Extremity 700 

The  Superficial  Lymphatic  Vessels   .      .  700 

The  Deep  Lymphatic  Vessels        .  .  701 


The  Lymphatics  of  the  Lower  Extremity. 

The  Lymph  Glands  of  the  Lower  Extremity  701 

The  Anterior  Tibial  Gland     ....  701 

The  Popliteal  Glands 701 

The  Inguinal  Glands 702 

The     Lymphatic     Vessels     of     the     Lower 

Extremity 703 

The  Superficial  Lymphatic  Vessels  .  703 

The  Deep  Lymphatic  Vessels      .  703 


The  Lymphatics  of  the  Abdomen  and  Pelvis. 

The  Lymph   Glands  of  the  Abdomen   and 

Pelvis 703 

The  Parietal  Glands 703 

The  External  Iliac  Glands  ...  703 
The  Common  Iliac  Glands  .      .  704 

The  Epigastric  Glands  ....  704 
The  Iliac  Circumflex  Glands  .  .  704 
The  Hypogastric  Glands       .      .      .      704 

The  Sacral  Glands 704 

The  Lumbar  Glands        ....      705 
The  Lymphatic  Vessels  of  the  Abdomen  and 

Pelvis 706 

The  Superficial  Vessels 706 

The  Deep  Vessels 706 

The     Lymphatic     Vessels     of     the 
Perineum  and  External  Genitals       706 

The  Visceral  Glands 706 

706 
706 
706 
709 
709 
709 
709 
710 


The  Gastric  Glands   . 

The  Hepatic  Glands 

The  Pancreaticolienial  Glands 
The  Superior  Mesenteric  Glands 

The  Mesenteric  Glands  . 

The  Ileocolic  Glands 

The  Mesocolic  Glands     . 
The  Inferior  Mesenteric  Glands 
The  Lymphatic  Vessels  of  the  Abdominal 

and  Pelvic  Viscera 710 


The   Lymphatic  Vessels  of   the   Abdomina 
and  Pelvic  Viscera — 
The  Lymphatic  Vessels  of  the  Subdia- 
phragmatic Portions  of  the  Digestive 

Tube 

The  Lymphatic  Vessels  of  the  Stomach  710 
The  Lymphatic  Vessels  of  the  Duodenum  710 
The  Lymphatic  Vessels  of  the  Jejunum         _^^H 

and  Ileum ^^41^1 

The  Lymphatic  Vessels  of  the  Vermiform  !■  ^H 

Process  and  Cecum 710 

The  Lymphatic  Vessels  of  the  Colon  .  711 
The   Lymphatic   Vessels   of   the   Anus,  ^.^^ 

Anal  Canal,  and  Rectum      ....     ''^l^l^H 
The  Lymphatic  Vessels  of  the  Liver  ^^^^1^1 

The    Lymphatic    Vessels    of    the   Gall-         ^B^H 

bladder  '^^flH 

The  Lymphatic  Vessels  of  the  Pancreas     71^H^H 
The  Lymphatic  Vessels  of  the  Spleen  and         ^H^l 

Suprarenal  Glands 7lU^B 

The  Lymphatic  Vessels  of  the  Urinary 

Organs    . 712 

The     Lymphatic     Vessels     of     the 

Kidney 712 

The  Lymphatic  Vessels  of  the  Ureter     712 
The     Lymphatic     Vessels    of    the 

Bladder 712 

The     Lymphatic     Vessels     of    the 

Prostate 713 

The     Lymphatic     Vessels     of     the 

Urethra 713 

The  Lymphatic  Vessels  of  the  Repro- 
ductive Organs 713 

The     Lymphatic    Vessels     of    the 

Testes 713 

The     Lymphatic     Vessels     of    the 

Ductus  Deferens 713 

The  Lymphatic  Vessels  of  the  Ovary     714 
The     Lymphatic     Vessels     of     the 

Uterine  Tube 714 

The     Lymphatic     Vessels     of    the 

Uterus 714 

The     Lymphatic     Vessels     of     the 
Vagina 714 


The  Lymphatics  of  the  Thorax. 


The  Parietal  Lymph  Glands 715 

The  Sternal  Glands 715 

The  Intercostal  Glands 715 

The  Diaphragmatic  Glands    .      .  .715 

The    Superficial  Lymphatic   Vessels   of   the 

Thoracic  Wall 715 

The  Lymphatic  Vessels  of  the  Mamma.  715 

The  Deep  Lymphatic  Vessels  of  the  Thoracic 

Wall 716 

The  Visceral  Lymph  Glands        .      .      .717 

The  Anterior  Mediastinal  Glands     .      .  717 
The  Posterior  Mediastinal  Glands    .      .717 

The  Tracheobronchial  Glands      .      .      .  717 

The    Lymphatic    Vessels    of    the    Thoracic 

Viscera 718 

The  Lymphatic  Vessels  of  the  Heart  .  718 
The  Lymphatic  Vessels  of  the  Lungs  .  718 
The  Lymphatic  Vessels  of  the  Pleura  719 
The  Lymphatic  Vessels  of  the  Thymus  719 
The  Lymphatic  Vessels  of  the  Eso- 
phagus        719 


NEUROLOGY. 


Structure  of  the  Nervous  System. 

Neuroglia 722 

Nerve  Cells 722 

Nerve  Fibers 724 

Wallerian  Degeneration 727 

Non-medullated  Fibers 728 

Structure    of     the    Peripheral    Nerves    and 

Ganglia ,  .v      •      •      •      '  Z^^ 

Origins  and  Terminations  of  Nerves   .      .      .  729 


Ganglia  

Neuron  Theory         

Fasciculi,  Tracts  or  Fiber  Systems 


730 
732 
732 


Development  of  the  Nervous  System. 

The  Medulla  Spinalis 733 

The  Spinal  Nerves 735 

The  Brain 736 


CONTENTS 


21 


The  Brain — 

The  Hind-brain  or  Rhombencephalon    .  738 

The  Mid-brain  or  Mesencephalon      .  741 

The  Fore-brain  or  Prosencephalon  741 

The  Diencephalon 742 

The  Telencephalon 743 

The  Commissures 746 

Fissures  and  Sulci 747 

The  Cranial  Nerves ".  748 


The  Spinal  Cord  or  Medulla  Spinalis. 

Enlargements 751 

Fissures  and  Sulci 752 

The  Anterior  Median  Fissure  752 

The  Posterior  Median  Sulcus  .  752 

The     Internal    Structure    of    the     Medulla 

Spinalis 753 

The  Gray  Substance 753 

Structure  of  the  Gray  Substance  755 

The  White  Substance 758 

Nerve  Fasciculi 759 

Roots  of  the  Spinal  Nerves 764 

The  Anterior  Nerve  Root       ....  764 

The  Posterior  Root 764 


The  Brain  or  Encephalon. 
General  Considerations  and  Divisions 


766 


The  Hind-brain  or  Rhombencephalon. 

The  Medulla  Oblongata 767 

The  Anterior  Median  Fissure             .  767 

The  Posterior  Median  Fissure     .      .      .  767 
Internal     Structure     of     the     Medulla 

Oblongata 775 

The  Cerebrospinal  Fasciculi  775 
Gray    Substance    of    the    Medulla 

Oblongata 779 

Inferior  Peduncle 782 

Formatio  Reticularis       ....  784 

The  Pons 785 

Structure                        785 

The  Cerebellum 788 

Lobes  of  the  Cerebellum 788 

Internal  Structure  of  the  Cerebellum  791 
The  White  Substance      .      .      .      .791 
Projection  Fibres                        .791 

The  Gray  Substance        ....  794 
Microscopic     Appearance     of     the 

Cortex 794 

The  Fourth  Ventricle    ....!!!  797 

Angles 797 

Lateral  Boundaries 797 

Choroid  Plexuses 798 

Openings  in  the  Roof 798 

Rhomboid  Fossa 798 

The  Mid-brain  or  Mesencephalon. 

The  Cerebral  Peduncles 800 

Structure  of  the  Cerebral  Peduncles       .  801 

The  Gray  Substance        ....  802 

The  White  Substance      ....  803 

The  Corpora  Quadrigemina 805 

Structure  of  the  Corpora  Quadrigemina  806 

The  Cerebral  Aqueduct 806 

The  Fore-brain  or  Prosencephalon. 

The  Diencephalon 807 

The  Thalamencephalon 808 

Structure 810 

Connections 810 

The  Metathalamus 811 

The  Epithalamus 812 

The  Hypothalamus 812 

The  Optic  Chiasma 814 

The  Optic  Tracts 814 

The  Third  Ventricle 815 

The  Interpeduncular  Fossa    .      .      .      .816 

The  Telencephalon 817 


The  Cerebral  Hemispheres 817 

The  Longitudinal  Cerebral  Fissure  .  818 
The    Surfaces   of    the    Cerebral    Hemi- 
spheres       818 

The  Lateral  Cerebral  Fissure       .  .  819 

The  Central  Sulcus 819 

The  Parietooccipital  Fissure  ....  820 

The  Calcarine  Fissure 820 

The  Cingulate  Sulcus 820 

The  Collateral  Fissure 820 

The  Sulcus  Circularis 821 

The  Lobes  of  the  Hemispheres    .      .      .  821 

The  Frontal  Lobe 821 

The  Parietal  Lobe 822 

The  Occipital  Lobe 823 

The  Temporal  Lobe 823 

The  Insula 825 

The  Limbic  Lobe 825 

The  Rhinencephalon 826 

The  Olfactory  Lobe   .....  826 
The    Interior    of    the    Cerebral    Hemi- 
spheres    827 

The  Corpus  Callosum      ....  828 

The  Lateral  Ventricles    ....  829 

The  Fornix 838 

The  Interventricular  Foramen  .  840 

The  Anterior  Commissure    .  840 

The  Septum  Pellucidum ....  840 
The  Choroid  Plexus  of  the  Lateral 

Ventricle 840 

Structure    of   the    Cerebral   Hemi- 
spheres   ■.      .  842 

Structure  of  the  Cerebral  Cortex  .  845 

Special  Types  of  Cerebral  Cortex      .      .  847 

Weight  of  Encephalon 848 

Cerebral  Localization 849 

Composition  and  Central  Connections  of  the  Spinal 
Nerves. 

The  Intrinsic  Spinal  Reflex  Paths       .      .  850 
Sensory  Pathways  from  the  Spinal  Cord 

to  the  Brain         851 

Composition  and  Central  Connections  of  the  Cranial 

Nerves. 

The  Hypoglossal  Nerve 855 

The  Accessory  Nerve 855 

The  Vagus  Nerve 855 

The  Glossopharyngeal  Nerve 856 

The  Acoustic  Nerve 857 

The  Vestibular  Nerve 860 

The  Facial  Nerve 861 

The  Abducens  Nerve 861 

The  Trigeminal  Nerve         862 

The  Trochlear  Nerve .  863 

The  Oculomotor  Nerve 863 

The  Optic  Nerve 864 

The  Olfactory  Nerves 866 

Pathways  from  the  Brain  to  the  Spinal  Cord. 

The  Motor  Tract 870 

The  Meninges  of  the  Brain  and  Medulla  Spinalis. 

The  Dura  Mater 872 

The  Cranial  Dura  Mater         ....  872 

Processes 873 

Structure 875 

The  Spinal  Dura  Mater 875 

Structure 876 

The  Arachnoid   . 876 

The  Cranial  Part 876 

The  Spinal  Part 876 

Structure 876 

The  Subarachnoid  Cavity      ....  876 

The  Subarachnoid  Cistemse  ....  876 

The  Arachnoid  Villi 878 

Structure 878 

The  Pia  Mater 878 

The  Cranial  Pia  Mater 879 

The  Spinal  Pia  Mater 879 

The  Ligamentum  Denticulatum        .  880 


22 


CONTENTS 


The  Cerebrospinal  Fluid 

The  Cranial  Nerves. 
The  Olfactory  Nerves 
The  Optic  Nerve. 


The  Optic  Chiasma 
The  Optic  Tract 


The  Oculomotor  Nerve 
The  Trochlear  Nerve     . 
The  Trigeminal  Nerve. 


The  Semilunar  Ganglion     . 
The  Ophthalmic  Nerve 

The  Lacrimal  Nerve    . 

The  Frontal  Nerve 

The  Nasociliary  Nerve 

The  Ciliary  Ganglion  . 
The  Maxillary  Nerve     . 

Branches      .... 

The  Middle  Meningeal  Nerve 
The  Zygomatic  Nerve     . 
The  Sphenopalatine  . 
The  Posterior  Superior  Alveolar 
The  Middle  Superior  Alveolar 
The  Anterior  Superior  Alveolar 
The  Inferior  Palpebral    . 
The  External  Nasal   . 
The  Superior  Labial 
The  Sphenopalatine  Ganglion 
The  Mandibular  Nerve       .... 

Branches      .  .      . 

The  Nervus  Spinosus 
The  Internal  Pterygoid  Nerve 
The  Masseteric  Nerve     . 
The  Deep  Temporal  Nerves 
The  Buccinator  Nerve     . 
The  External  Pterygoid  Nerve 
The  Auriculotemporal  Nerve 
The  Lingual  Nerve    . 
The  Inferior  Alveolar  Nerve 
The  Otic  Ganglion     . 
The  Submaxillary  Ganglion 
Trigeminal  Nerve  Reflexes 


The  Abducent  Nerve 
The  Facial  Nerve. 


880 


881 


883 

884 


885 


886 

887 
887 
887 

888 


890 
890 
891 
891 
891 
891 
891 
891 
893 
894 
894 
894 
894 
895 
895 
895 
895 
895 
896 
897 
898 
899 

899 


The  Greater  Superficial  Petrosal  Nerve  .      .  903 

The  Nerve  to  the  Stapedius 904 

The  Chorda  Tympani  Nerve 904 

The  Posterior  Auricular  Nerve      ....  905 

The  Digastric  Branch 905 

The  Stylohyoid  Branch 905 

The  Temporal  Branches 905 

The  Zygomatic  Branches 905 

The  Buccal  Branches 905 

The  Mandibular  Branch 905 

The  Cervical  Branch 905 

The  Acoustic  Nerve. 

The  Cochlear  Nerve 906 

The  Vestibular  Nerve 906 


The  Ganglion  Nodosum — 

The  Meningeal  Branch      . 

The  Auricular  Branch 

The  Pharyngeal  Branch    . 

The  Superior  Laryngeal  Nerve 

The  Recurrent  Nerve 

The  Superior  Cardiac  Branches 

The  Inferior  Cardiac  Branches 

The  Anterior  Bronchial  Branches 

The  Posterior  Bronchial  Branches 

The  Esophageal  Branches 

The  Gastric  Branches 

The  Celiac  Branches 

The  Hepatic  Branches 


The  Accessory  Nerve, 


The  Cranial  Part 
The  Spinal  Part 


The  Hypoglossal  Nerve. 


The  Glossopharyngeal  Nerve. 

The  Superior  Ganglion        .... 

The  Petrous  Ganglion 

The  Tympanic  Nerve 
The  Carotid  Branches 
The  Pharyngeal  Branches 


908 
908 
909 
909 
909 


The  Muscular  Branches 909 

The  Tonsillar  Branches 909 

The  Lingual  Branches 909 

The  Vagus  Nerve. 

The  Jugular  Ganglion 911 

The  Ganglion  Nodosum 911 


Branches  of  Communication 
Branches  of  Distribution    . 
The  Meningeal  Branches 
The  Descending  Ramus 
The  Thyrohyoid  Branch 
The  Muscular  Branches 


The  Spinal  Nerves. 

Nerve  Roots 

The  Anterior  Root 

The  Posterior  Root 

The  Spinal  Ganglia 

Structure 

Connections  -with  Sympathetic     . 

Structure 

Divisions  of  the  Spinal  Nerves      .... 

The  Posterior  Divisions 

The  Cervical  Nerves  .... 
The  Thoracic  Nerves  .... 
The  Lumbar  Nerves        .... 

The  Sacral  Nerves 

The  Coccygeal  Nerve      .... 

The  Anterior  Divisions 

The  Cervical  Nerves        .... 
The  Cervical  Plexus 

Great  Auricular  Nerve 
Cutaneous  Cervical  Nerve 
Supraclavicular  Nerves     . 
Communicantes  Cervicales 
Phrenic  Nerve  .... 
The  Brachial  Plexus 

Relations 

Dorsal  Scapular  Nerve     . 
Suprascapular  Nerve  . 
Nerve  to  Subclavius    . 
Long  Thoracic  Nerve 
Anterior  Thoracic  Nerves 
Subscapular  Nerves     . 
Thoracodorsal  Nerve  . 
Axillary  Nerve 
Musculocutaneous  Nerve 
Medial  Antibrachial  Cuta- 
neous Nerve 
Medial  Brachial  Cuta- 
neous Nerve 
Median  Nerve  . 
Ulnar  Nerve 
Radial  Nerve    . 
The  Thoracic  Nerves 

First  Thoracic  Nerve 
Upper  Thoracic  Nerves 
Lower  Thoracic  Nerves 
The  Lumbosacral  Plexus 
The  Lumbar  Nerves 

The  Lumbar  Plexus 

Iliohypogastric  Nerve 
Ilioinguinal  Nerve 
Genitofemoral  Nerve 
Lateral  Femoral  Cuta- 
neous Nerve 
Obturator  Nerve 


911 
911 
911 
912 
912 
912 
912 
913 
913 
913 
913 
913 
913 


913 
913 


915 
916 
916 
916 
916 
916 


916 
916 
916 
917 
917 
920 
920 
921 
921 
921 
923 
924 
924 
925 
925 
925 
925 
926 
927 
928 
928 
928 
930 
931 
932 
932 
933 
933 
933 
933 
934 
934 
935 

937 

937 
938 
939 
943 
944 
945 
945 
948 
948 
948 
949 
950 
952 
953 

953 
953 


CONTENTS 


23 


Divisions  of  the  Spinal  Nerves — 
The  Anterior  Divisions — 

The  Lumbosacral  Plexus — 
The  Lumbar  Nerves — 

The  Lumbar  Plexus — 

Accessory     Obturator 

Nerve     ....     955 
Femoral  Nerve     .  955 

Saphenous  Nerve.  956 

The    Sacral    and    Coccygeal 

Nerves 957 

The  Sacral  Ple.xus  957 

Relations        .  957 

Nerve  to  Quadratus 
Femoris     and 
Gemellus  Inferior        957 
Nerve  to  Obturator 
Internus  and   Ge- 
mellus Superior     .       958 
Nerve  to  Piriformis         959 
Superior     Gluteal 

Nerve   ....        959 
Inferior     Gluteal 

Nerve  ....        959  ; 
Posterior       Femoral  j 

Cutaneous  Nerve         959  j 
Sciatic  Nerve      .      .        960 
Tibial  Nerve       .      .       960 
Lateral  Plantar  Nerve     963 
Common      Peroneal 

Nerve     ....     964 
Deep  Peroneal  Nerve    965 
Superficial      Peroneal 
Nerve     ....     966 
The  Pudendal  Plexus  966 

Perforating  Cuta- 

neous Nerve      .      .     967 
Pudendal  Nerve  .     967 

Anococcygeal     Nerve     968 


The  Sympathetic  Nerves. 

The  Cranial  Sympathetics 970 

The  Sacral  Sympathetics 973 

The  Thoracolumbar  Sympathetics      .      .      .  974 

The  Sympathetic  Trunks  976 

Connections  with  the  Spinal  Nerves         .  976 

Development 977 


The  Cephalic  Portion  of  the  Sympathetic 
System. 


The  Internal  Carotid  Plexus 
The  Cavernous  Plexus 


977 
978 


The  Cervical  Portion  of  the  Sympathetic 
System. 


The  Superior  Cervical  Ganglion 
Branches    

The  Middle  Cervical  Ganglion 
Branches    

The  Inferior  Cervical  Ganglion 
Branches    


978 
978 
979 
979 
980 
981 


The   Thoracic  Portion  of  the  Sympathetic 

System. 

The  Greater  Splanchnic  Nerve    ....  981 

The  Lesser  Splanchnic  Nerve       ....  981 

The  Lowest  Splanchnic  Nerve     ....  981 

The  Abdominal  Portion  of  the  Sympathetic 

System  ....  982 

The  Pelvic  Portion  of  the  Sympathetic 

System  ....  984 

The  Great  Plexuses  of  the  Sympathetic  System. 

The  Cardiac  Plexus 984 

The  Celiac  Plexus  985 

,  Phrenic  Plexus 985 

*  Hepatic  Plexus 986 

Lienal  Plexus  986 

Superior  Gastric  Plexus 987 

Suprarenal  Plexus 987 

Renal  Plexus 987 

Spermatic  Plexus  987 

Superior  Mesenteric  Plexus  .      .      .  987 

Abdominal  A^tic  Plexus        ....  987 

Inferior  Mesenteric  Plexus     ....  987 

The  Hypogastric  Plexus 987 

The  Pelvic  Plexuses 987 

The  Middle  Hemorrhoidal  Plexus     .      .  988 

The  Vesical  Plexus 988 

The  Prostatic  Plexus 988 

The  Vaginal  Plexus 989 

The  Uterine  Plexus 989 


THE  ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT. 


The  Peripheral  Organs  of  the  Special 

Senses. 

The  Organs  of  Taste. 

Structure 991 

The  Organ  of  Smell. 

The  External  Nose 992 

Structure 992 

The  Nasal  Cavity 994 

The  Lateral  Wall 994 

The  Medial  Wall 995 

The  Mucous  Membrane  ....  996 
Structure 996 

The  Accessory  Sinuses  of  the  Nose  .  998 

The  Frontal  Sinuses 998 

The  Ethmoidal  Air  Cells      ....       998 

The  Sphenoidal  Sinuses 998 

The  Maxillary  Sinus 999 

The  Organ  of  Sight. 

Development 1001 

The  Tunics  of  the  Eye 1005 

The  Fibrous  Tunic 1005 

The  Sclera 1005 

Structure 1006 

The  Cornea 1006 

Structure 1007 


The  Tunics  of  the  Eye — 

The  Vascular  Tunic 1009 

The  Choroid 1009 

Structure 1010 

The  Ciliary  Body 1010 

Structure 1011 

The  Iris 1012 

Structure 1013 

Membrana  Pupillaris     ....  1014 

The  Retina 1014 

Structure 1015 

The  Refracting  Media 1018 

The  Aqueous  Humor 1018 

The  Vitreous  Bodv 1018 

The  Crystalline  Lens 1019 

Structure 1020 

The  Accessory  Organs  of  the  Eye     .  1021 

The  Ocular  Muscles 1021 

Levator  PalpebrEe  Superioris    .  1021 

The  Recti 1022 

Obliquus  Oculi  Superior      .      .      .  1022 

Obliquus  Oculi  Inferior       .      .      .  1023 

The  Fascia  Bulb 1024 

The  Orbital  Fascia 1025 

The  Eyebrows 1025 

The  Eyelids 1025 

The    Lateral    Palpebral    Commis- 
sure         1025 

The  Eyelashes 1025 

Structure  of  the  Eyelids    .      .  1025 

The  Tarsal  Glands 1026 


24 


CONTENTS 


The  Accessory  Organs  of  the  Eye — 

Structure  of  the  Tarsal  Glands 
The  Conjunctiva 

The  Palpebral  Portion 
The  Bulbar  Portion 
The  Lacrimal  Apparatus 
The  Lacrimal  Gland 

Structure 
The  Lacrimal  Ducts 
The  Lacrimal  Sac 

Structure 
The  Nasolacrimal  Duct 

The  Organ  of  Hearing. 


1026 
1026 
1027 
1027 
1028 
1028 
1028 
1028 
1028 
1029 
1029 


Development 1029 

The  External  Ear 1033 

The  Auricula  or  Pinna 1033 

Structure 1034 

The  External  Acoustic  Meatus        .      .  1036 

Relations 1037 

The  Middle  Ear  or  Tympanic  Cavity    .      .  1037 

The  Tegumental  Wall  or  Roof  .      .      .  1038 

The  Jugular  Wall  or  Floor   ....  1038 

The  Membranous  or  Lateral  Wall         .  1038 

The  Tympanic  Membrane    ....  1039 

Structure 1039 

The  Labyrinthic  or  Medial  Wall     .      .  1040 

The  Mastoid  or  Posterior  Wall        .      .  1042 

The  Carotid  or  Anterior  Wall    .      .      .  1042 

The  Auditory  Tube 1042 

The  Auditory  Ossicles 1044 

The  Malleus X044 

The  Incus 1044 

The  Stapes 1045 

Articulations  of  the  Auditory  Ossicles  1045 

Ligaments  of  the  Ossicles     ....  1045 

The  Muscles  of  the  Tympanic  Cavity  1046 

The  Tensor  Tympani    ....  1046 

The  Stapedius     .      .  , .      .      .      .  1046 

The  Internal  Ear  or  Labyrinth    ....  1047 

The  Osseous  Labyrinth 1047 


The  Internal  Ear  or  Labyrinth — 
The  Osseous  Labyrinth — 

The  Vestibule 

The  Bony  Semicircular  Canals 
The  Cochlea  .  .  . 
The  Membranous  Labyrinth 
The  Utricle  .... 
The  Saccule  .... 
The  Semicircular  Ducts 

Structure 
The  Ductus  Cochlearis 
The  Basilar  Membrane 
The  Spiral  Organ  of  Corti 
Hair  Cells      .... 


1047 
1049 
1050 
1051 
1051 
1052 
1052 
1052 
1054 
1056 
1056 
1057 


Peripheral  Terminations  of  Nerves  of  General 
Sensations. 

Free  Nerve-endings 1059 

Special  End-organs 1059 

End-bulbs  of  Krause 1060 

Tactile  Corpuscles  of  Grandry     ....  1060 

Pacinian  Corpuscles 1060 

Corpuscles  of  Golgi  and  Mazzoni      .      .      .  1061 

Tactile  Corpuscles  of  Wagner  and  Meissner  1061 

Corpuscles  of  Ruffini 1061 

Neurotendinous  Spindles 1061 

Neuromuscular  Spindles 1061 


The  Comon  Integument. 

The  Epidermis,  Cuticle,  or  Scarf  Skin     .      .  1062 
The  Corium,  Cutis  Vera,  Dermis,  or  True 

Skin 1065 

Development 1066 

The  Appendages  of  the  Skin. 

The  Nails 1066 

The  Hairs 1067 

The  Sebaceous  Glands 1069 

The  Sudoriferous  or  Sweat  Glands   .      .      .  1070 


I 


SPLANCHNOLOGY. 


The  Respiratory  Apparatus. 


Development 

1071 

The  Larynx. 

The  Cartilages  of  the  Larynx      ....     1073 

The  Thyroid  Cartilage    . 

1073 

The  Cricoid  Cartilage 

1074 

The  Arytenoid  Cartilage 

1075 

The  Corniculate  Cartilages 

1075 

The  Cuneiform  Cartilages 

1075 

The  Epiglottis      .      .      . 

1075 

Structure 

1076 

The  Ligaments  of  the  Larynx 

1076 

The  Extrinsic  Ligaments 

1076 

The  Intrinsic  Ligaments 

1077 

The  Interior  of  the  Larynx     . 

1078 

The  Ventricular  Folds 

1079 

The  Vocal  Folds  .      .      . 

1079 

The  Ventricle  of  the  Larynx 

1080 

The  Rima  Glottidis   .      . 

1080 

The  Muscles  of  the  Larynx    . 

1081 

Cricothyreoideus 

1081 

Cricoarytsenoideus  Posterior 

1082 

Cricoarytsenoideus  Lateralis 

1082 

Arytsenoideus        .... 

1082 

Thyreoarytsenoideus 

1083 

The  Trachea  and  Bronchi. 

Relations 1084 

The  Right  Bronchus 1085 

The  Left  Bronchus        .......  1085 

Structure 1086 


The  Pleurce. 

Reflections  of  the  Pleura 1088 

Pulmonary  Ligament 1090 

Structure  of  Pleura 1090 

The  Mediastinum. 

Superior  Mediastinum 1090 

Anterior  Mediastinum 1092 

Middle  Mediastinum .  1092 

Posterior  Mediastinum 1093 

The  Lungs. 

The  Apex  of  the  Lungs 1094 

The  Base  of  the  Lungs 1094 

Surfaces  of  the  Lungs 1094 

Borders  of  the  Lungs 1096 

Fissures  and  Lobes  of  the  Lungs       .      .      .  1096 

The  Root  of  the  Lung 1097 

Divisions  of  the  Bronchi 1097 

Structure  of  the  Lungs 1098 

The  Digestive  Apparatus. 

The  Digestive  Tube 1100 

The    Development    of     the    Digestive 

Tube 1101 

The  Mouth 1101 

The  Salivary  Glands      ....  1102 

The  Tongue         1102 

The  Palatine  Tonsils  ....  1103 
The  Further  Development  of  the 

Digestive  Tube 1103 

The  Rectum  and  Anal  Canal   .      .  1 108 


CONTENTS 


25 


The  Mouth. 


The  Abdomen. 


The  Vestibule  of  the  Mouth 1110 

The  Mouth  Cavity  Proper 1110 

Structure 1110 

The  Lips 1111 

The  Labial  Glands 1111 

The  Cheeks 1112 

Structure 1112 

The  Gums 1112 

The  Palate 1112 

The  Hard  Palate 1112 

The  Soft  Palate 1112 

The  Teeth 1112 

General  Characteristics 1114 

The  Permanent  Teeth 1115 

The  Canine  Teeth 1117 

The  Premolar  or  Bicuspid  Teeth  .  1118 

The  Molar  Teeth 1118 

The  Deciduous  Teeth 1118 

Structure  of  the  Teeth 1118 

Development  of  the  Teeth    ....  1121 
Development    of    the    Deciduous 

Teeth 1122 

Development   of    the    Permanent 

Teeth 1124 

Eruption  of  the  Teeth     .      .      .      .  1124 

The  Tongue 1125 

The  Root  of  the  Tongue       ....  1125 

The  Apex  of  the  Tongue       .      .      .  1125 

The  Dorsum  of  the  Tongue        .      .      .  1125 

The  Papilla;  of  the  Tongue  .       .      .      .  1126 

The  Muscles  of  the  Tongue        .      .      .  1128 

Genioglossus 1129 

Hyoglossus 1129 

Chondroglossus 1130 

Styloglossus 1130 

Longitudinalis  Linguae  Superior  1130 

Longitudinalis  Linguae  Inferior  1130 

Transversus  Linguae      .      .      .      .  1130 

Verticalis  Linguae 1131 

Structure  of  the  Tongue              .      .  1131 

Glands  of  the  Tongue 1131 

The  Salivary  Glands 1132 

The  Parotid  Gland 1132 

Structures  within  the  Gland     .      .  1134 

The  Parotid  Duct 1134 

Structure 1134 

The  Submaxillary  Gland       ....  1135 

The  Submaxillary  Duct             .      .  1135 

The  Sublingual  Gland 1136 

Structure  of  the  Salivary  Gland            .  1136 

Accessory  Glands 1137 

The  Fauces. 


The  Glossopalatine  Arch 

1137 

The  Pharyngopalatine  Arch    . 

1137 

The  Palatine  Tonsils    .      .      . 

1137 

Structure 

1139 

The  Palatine  Aponeurosis 

1139 

The  Muscles  of  the  Palate 

1139 

Levator  Veli  Palatini 

1139 

Tensor  Veli  Palatini 

1139 

Musctilus  Uvulae 

1139 

Glossopalatinus 

1139 

Paryngopalatinus 

1139 

The  Pharynx. 

The  Nasal  Part  of  the  Pharynx  ....      1141 

The  Oral  Part  of  the  Pharynx     .      . 

1142 

The  Laryngeal  Part  of  the  Pharynx 

1142 

The  Muscles  of  the  Pharynx 

1142 

Constrictor  Pharyngis  Inferior  . 

1142 

Constrictor  Pharyngis  Medius  . 

1142 

Constrictor  Pharyngis  Superior 

1142 

Stylopharyngeus 

1142 

Salpingopharyngeus  . 

1142 

Structure  of  the  Pharynx 

1143 

The  Esopfiagus. 

Relations 

1145 
1146 

Structure 

Boundaries  of  the  Abdomen  .....  1147 

The  Apertures  in  the  Walls  of  the  Abdomen  1147 

Regions  of  the  Abdomen 1147 

The  Peritoneum 1149 

Vertical  Dispositions  of  the  Main  Peri- 
toneal Cavity 1150 

Vertical    Disposition    of    the    Omental 

Bursa 1152 

Horizontal    Disposition    of    the    Peri- 
toneum         1153 

In  the  Pelvis       .      .      .  .  1153 

In  the  Lower  Abdomen  1154 

In  the  Upper  Abdomen  .      .  1155 

The  Omenta 1156 

The  Mesenteries 1157 

The  Peritoneal  Recesses  or  Fossae  .      .  1158 

The  Duodenal  Fossae     ....  1159 

The  Cecal  Fossae 1160 

The  Intersigmoid  Fossa      .      .      .  1161 

Th^  Stomach. 

Openings  of  the  Stomach 1161 

Curvatures  of  the  Stomach 1162 

Surfaces  of  the  Stomach 1162 

Component  Parts  of  the  Stomach     .      .      .  1163 

Position  of  the  Stomach 1163 

Interior  of  the  Stomach 1164 

Pyloric  Valve *    .      .      .  1164 

Structure  of  the  Stomach 1164 

The  Gastric  Glands 1166 

The  Small  Intestine. 

The  Duodenum 1169 

Relations     .  1169 

The  Jejunum  and  Ileum 1170 

Meckel's  Diverticulum 1172 

Structure 1172 

The  Large  Intestine. 

The  Cecum 1177 

The  Vermiform  Process  or  Appendix  .  1178 

Structure 1179 

The  Colic  Valve 1179 

The  Colon 1180 

The  Ascending  Colon 1180 

The  Transverse  Colon 1180 

The  Descending  Colon 1181 

The  Iliac  Colon 1182 

The  Sigmoid  Colon 1182 

The  Rectum 1183 

Relations  of  the  Rectum       ....  1184 

The  Anal  Canal 1184 

Structure  of  the  Colon 1184 

The  Liver. 

Surfaces  of  the  Liver 1188 

Fossae  of  the  Liver 1191 

Lobes  of  the  Liver 1191 

Ligaments  of  the  Liver 1192 

Fixation  of  the  Liver 1193 

Development  of  the  Liver 1 193 

Structure  of  the  Liver  .      .      .      .  1195 

Excretory  Apparatus  of  the  Liver     .      .      .  1197 

The  Hepatic  Duct 1197 

The  Gall-bladder 1197 

Relations .  1197 

Structure 1198 

The  Common  BUe  Duct       ....  1198 

Structure 1199 

The  Pancreas. 

Relations 1200 

The  Pancreatic  Duct 1202 

Development  of  the  Pancreas      ....  1202 

Structure 1203 


26 


CONTENTS 


The  Urogenital  Apparatus. 


Development  of  the.  Urinary  and  Generative  Organs 

The  Pronephros  and  Wolffian  Duct        .      .  1205 
The    Mesonephros,     Milllerian    Duct,    and 

Genital  Gland 1205 

The  Miillerian  Ducts 1206 

Genital  Glands 1207 

The  Ovary         1207 

The  Testis 1210 

Descent  of  the  Ovaries 1211 

The     Metanephros      and     the     Permanent 

Kidney 1211 

The  Urinary  Bladder         1212 

The  Prostate 1213 

External  Organs  of  Generation  .  1213 

The  Urethra 1215 

The  Urinary  Organs. 

The  Kidneys 1215 

Relations 1215 

Surfaces 1215 

Borders 1218 

Extremities 1219 

Fixation  of  the  Kidney  ....  1220 

General  Structure  of  the  Kidney  .  1220 

The  Ureters 1225 

The  Ureter  Proper 1226 

Structure   .  , 1227 

Variations    ' 1227 

The  Urinary  Bladder 1227 

The  Empty  Bladder 1227 

The  Distended  Bladder 1228 

The  Bladder  in  the  Child      ....  1229 

The  Female  Bladder 1230 

The  Ligaments  of  the  Bladder  .      .      .  1231 

The  Interior  of  the  Bladder        .      .      .  1231 

Structure 1232 

Abnormalities 1233 

The  Male  Urethra 1234 

The  Prostatic  Portion 1234 

The  Membranous  Portion    ....  1235 

The  Cavernous  Portion 1235 

Structure 1235 

Congenital  Defects 1235 

The  Female  Urethra 1236 

Structure 1236 

Th  Male  Genital  Organs. 

The  Testes  and  their  Coverings  ....  1236 

The  Scrotum 1237 

The  Intercrural  Fascia 1238 

The  Cremaster  Muscle 1238 

The  Infundibuliform  Fascia       .      .      .  1239 

The  Tunica  Vaginalis 1239 

The  Inguinal  Canal 1239 

The  Spermatic  Cord 1239 

Structure  of  the  Spermatic  Cord  .  1239 

The  Testes 1240 

The  Epididymis 1242 

Appendages  of  the  Testis  and  Epi- 
didymis      1242 

The  Tunica  Vaginalis  .  1242 

The  Tunica  Albuginea  .  1242 

The  Tunica  Vasculosa  .  1243 

Structure 1243 

Peculiarities 1245 

The  Ductus  Deferens 1245 

The  Ductuli  Aberrantes        ....  1246 

Paradidymis 1246 

Structure 1246 

The  Vesiculse  Seminales 1246 

Structure 1247 

The  Ejaculatory  Ducts     ......  1247 

Structure 1247 

The  Penis 1247 

The  Corpora  Cavernosa  Penis  .      .      .  1248 

The  Corpus  Cavernosum  Urethrse        .  1248 

Structure  of  the  Penis 1250 


The  Prostate     .      .      .     ^^^^^^H"    .  1251 

Structure   .      .      .     ^^^^^^K     •  1253 

The  Bulbourethral  Glands 1253 

Structure 1253 

The  Female  Genital  Organs. 

The  Ovaries 1254 

The  Epoophoron 1255 

The  Paroophoron 1255 

Structure 1255 

Vesicular  Ovarian  Follicles  ....  125& 

Discharge  of  the  OvuVn 1256 

Corpus  Luteum 1256 

The  Uterine  Tube 1257 

Structure 1257 

The  Uterus 1258 

The  Body 1259 

The  Cervix 1259 

The  Interior  of  the  Uterus   ....  1260 

The  Cavity  of  the  Body      .      .      .  1260 

The  Canal  of  the  Cer\ax      .      .      .  1260 

The  Ligaments  of  the  Uterus     .      .      .  1260 

Structure 1262 

The  Vagina 1264 

Relations 1264 

Structure 1264 

The  External  Organs 1264 

The  Mons  Pubis 1265 

The  Labia  Majora 1265 

The  Labia  Minora 1265 

The  Clitoris 1266 

The  Vestibule 1266 

The  Bulb  of  the  Vestibule    ....  1266 

The  Greater  Vestibular  Glands  .  1266 

The  Mammae 1267 

The  Mammary  Papilla  or  Nipple  .  1267 

Development         1267 

Structure 1267 


The  Ductle.ss  Glands. 

The  Thyroid  Gland. 

Development  1270 

Structure 1271 

The  Parathyroid  Glands. 

Development     .  1272 

Structure 1273 

The  Thymus. 

Development 1273 

Structure 1274 

The  Hypophysis  Cerebri. 

Development 1276 

The  Pineal  Body. 

Structure 1277 

The  Chromaphil  and  Cortical  Systems. 

Development 1277 

The  Suprarenal  Glands 1278 

Development         1278 

Relations 1278 

Accessory  Suprarenals 1279 

Structure 1279 

Glomus  Caroticum 1281 

Glomus  Coccygeum 1281 

The  Spleen. 

Development 1282 

Relation 1282 

Structure 1283 


STENTS 


27 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS. 


Surface  Anatomy  of  the  Head  and  Neck. 

The  Bones 1287 

The  Joints  and  Muscles          1288 

THe  Arteries 1290 

Surface  Markings  of  Special  Regions  of  the  Head 
and  Meek. 

The  Cranium 1291 

The  Scalp 1291 

Bony  Landmarks 1291 

The  Brain 1292 

Vessels              1294 

The  Face 1294 

External  Maxillary  Artery   ....  1294 

Trigeminal  Nerve 1295 

Parotid.  Gland 1295 

The  Nose 1296 

The  Mouth 1296 

The  Eye 1299 

The  Ear 1300 

The  Tympanic  Antrum 1301 

The  Neck 1301 

Muscles 1302 

Arteries 1302 

Veins 1303 

Nerves 1303 

Submaxillary  Gland 1303 

Surface  Anatomy  of  the  Back. 

Bones 1303 

Muscles 1304 

Surface  Markings  of  the  Back. 

Bony  Landmarks 1305 

Medulla  Spinalis 1306 

Spinal  Nerves 1307 

Surface  Anatomy  of  the  Thorax. 

Bones 1307 

Muscles 1307 

Mamma \  1308 

Surface  Markings  of  the  Thorax. 

Bony  Landmarks 1308 

Diaphragm [      ]  I309 

Surface  Lines I3O9 

Pleurae          '      "  1309 

Lungs '.'.'.  1310 

Irachea 1311 

Esophagus [      [  1311 

Heart 1311 

Arteries \  1312 

Veins '\  1312 

Surface  Anatomy  of  the  Abdomen. 

|^'° 1313 

?oiies 1313 

Musces 1313 

^?ssels 1313 

Viscera I313 


Surface  Markings  of  the  Abdomen. 

Bony  Landmarks 1315 

Muscles 1315 

Surface  Lines 1315 

Stomach 1317 

Duodenum 1319 

Small  Intestine 1319 

Cecum  and  Vermiform  Process   ....  1319 

Ascending  Colon 1319 

Transverse  Colon 1319 

Descending  Colon 1320 

Iliac  Colon 1320 

Liver 1320 

Pancreas 1320 

Spleen           1320 

Kidneys 1320 

Ureters 1321 

Vessels 1321 

Nerves 1322 

Surface  Anatomy  of  the  Perineum. 

Skin 1322 

Bones 1322 

Muscles  and  Ligaments 1322 

Surface  Markings  of  the  Perineum. 

Rectum  and  Anal  Canal 1322 

Male  Urogenital  Organs    .      .                   .      .  1323 

Female  Urogenital  Organs 1323 

Surface  Anatomy  of  the  Upper  Extremity. 

Skin 1325 

Bones 1326 

Articulations 1327 

Muscles 1327 

Arteries 1331 

Veins 1331 

Nerves 1331 

Surface  Markings  of  the  Upper  Extremity. 

Bony  Landmarks 1331 

Articulations 1331 

Muscles 1332 

Mucous  Sheaths 1334 

Arteries 1334 

Nerves 1335 

Surface  Anatomy  of  the  Lower  Extremity. 

Skin 1336 

Bones 1336 

Articulations 1338 

Muscles 1338 

Arteries 1341 

Veins 1342 

Nerves 1342 

Surface  Markings  of  the  Lower  Extremity. 

Bony  Landmarks 1342 

Articulations 1343 

Muscles 1343 

Mucous  Sheaths 1343 

Arteries 1343 

Veins ]      .  1345 

Nerves 1346 


^^K^  ANATOMICAL  BIBLIOaRAPHY.        ^M 

^^^^^  INDEXES.  ^M 

Anatomical  Bibliography  of  the  Concilium  Bibliographiciim,  ^^^| 

Bibliographic  Service;  Wistar  Institute  of  Anatomy,  1917-         .  ^^^H 

Bibliographie  Anatomique,  1893-        .  fl 

Index  Medicus,  1879-  I 

Index  Catalogue  of  the  Library  of  the  Surgeon-General's  Office,  U.  S.  ArnB 

1880-  \ 

Jahresberichte  iiber  die  Fortschritte  der  Anatoraie  und  Physiologic,  1856-1894. 
Jahresberichte  iiber  die  Fortschritte  der  Anatomic  mid  Entwicklungsgeschichte, 

1895- 

JOURNALS. 

The  Anatomical  Record,  1906- 

The  American  Journal  of  Anatomy,  1901- 

Anatomische  Hefte,  1892- 

Anatomischer  Anzeiger,  1886- 

Archives  d 'Anatomic  Microscopique,  1897- 

Archiv  fiir  Anatomic  und  Physiologic,  1795- 

Archiv  fiir  Entwicklungsmechanik  der  Organismen,  1894- 

Archiv  fiir  Microskopische  Anatomic,  1865- 

Archivo  Italiano  di  Anatomia  e  di  Embriologia,  1902- 

Biological  Bulletin,  1900- 

Brain,  1878- 

Bibliographie  Anatomique,  1893- 

Contributions  to  Embryology,  Carnegie  Institution  of  Washington,  1914-- 

Comptcs  Rendus  de  1' Association  des  Anatomistes,  1899- 

Gegenbaur's  Morphologischcs  Jahrbuch,  1876- 

International  Monatsschrift  fiir  Anatomic  und  Histologic,  1884- 

The  Journal  of  Anatomy  and  Physiology,  1867- 

Journal  of  Comparative  Neurology,  1891- 

. Journal  de  1 'Anatomic  et  de  Physiologic,  etc.,  1864- 

Journal  of  Experimental  Zoology,  1904- 

Journal  of  Morphology,  1887- 

Le  Nevraxe,  1900- 

Morphologischc  Arbciten,  1892-1898. 

Petrus  Camper  Nederlandschc  Bijdragen  tot  de  Anatomic,  1902- 

Proceedings  of  the  Royal  Society,  Scries  B. 

Quarterly  Journal  of  Microscopical  Science,  1853- 

Zcitschrift  fiir  Morphologic  und  Anthropologic,  1899- 

Zeitschrift  fiir  Wissenschaftliche  Mikroskopie,  1884- 


XXV  iii ) 


ANATOMY  OF  THE  HUMAN  BODY 


INTRODUCTION. 


THE  term  human  anatomy  comprises  a  consideration  of  the  various  structures 
which  make  up  the  human  organism.  In  a  restricted  sense  it  deals  merely 
with  the  parts  which  form  the  fully  developed  individual  and  which  can  be  ren- 
dered evident  to  the  naked  eye  by  various  methods  of  dissection.  Regarded  from 
such  a  standpoint  it  may  be  studied  by  two  methods:  (1)  the  various  structures 
may  be  separately  considered— systematic  anatomy;  or  (2)  the  organs  and  tissues 
may  be  studied  in  relation  to  one  another — topographical  or  regional  anatomy. 

It  is,  however,  of  much  advantage  to  add  to  the  facts  ascertained  by  naked- 
eye  dissection  those  obtained  by  the  use  of  the  microscope.  This  introduces 
two  fields  of  investigation,  viz.,  the  study  of  the  minute  structure  of  the  various 
component  parts  of  the  body — histology — and  the  study  of  the  human  organism 
in  its  immature  condition,  i.  e.,  the  various  stages  of  its  intrauterine  develop- 
ment from  the  fertilized  ovum  up  to  the  period  when  it  assumes  an  independent 
existence — embryology.  Owing  to  the  difficulty  of  obtaining  material  illustrating 
all  the  stages  of  this  early  development,  gaps  must  be  filled  up  by  observations 
on  the  development  of  lower  forms — comparative  embryology,  or  by  a  consideration 
of  adult  forms  in  the  line  of  human  ancestry — comparative  anatomy.  The  direct 
application  of  the  facts  of  human  anatomy  to  the  various  pathological  conditions 
which  may  occur  constitutes  the  subject  of  applied  anatomy.  Finally,  the  appre- 
ciation of  structures  on  or  immediately  underlying  the  surface  of  the  body  is 
frequently  made  the  subject  of  special  study — smiace  anatomy. 

Systematic  ANATOMY.^The  various  systems  of  which  the  human  body  is 
composed  are  grouped  under  the  following  headings: 

1.  Osteology — the  bony  system  or  skeleton. 

2.  Syndesmology — the  articulations  or  joints. 

3.  Myology — the  muscles.  With  the  description  of  the  muscles  it  is  convenient 
to  include  that  of  the  fasciae  which  are  so  intimately  connected  with  them. 

4.  Angiology — the  vascular  system,  comprising  the  heart,  bloodvessels,  lymphatic 
vessels,  and  lymph  glands. 

5.  Neurology — the  nervous  system.  The  organs  of  sense  may  be  included  in 
this  system. 

6.  Splanchnology  —  the  visceral  system.  Topographically  the  viscera  form 
two  groups,  viz.,  the  thoracic  viscera  and  the  abdomino-pelvic  viscera.  The 
heart,  a  thoracic  viscus,  is  best  considered  with  the  vascular  system.    The  rest 

3  (33) 


34 


INTRODUCTION 


I 


of  the  viscera  may  be  grouped  according  to  their  functions:  (a)  the  respiratory 
apparatus;  (6)  the  digestive  apparatus;  and  (c)  the  urogenital  apparatus.  Strictly 
speaking,  the  third  subgroup  should  include  only  such  components  of  the 
urogenital  apparatus  as  are  included  within  the  abdomino-pelvic  cavity,  but  it 
is  convenient  to  study  under  this  heading  certain  parts  which  lie  in  relation  to 
the  surface  of  the  body,  e.  g.,  the  testes  and  the  external  organs  of  generation. 

For  descriptive  purposes. the  body  is  supposed  to  be  in  the  erect  posture,  with 
the  arms  hanging  by  the  sides  and  the  palms  of  the  hands  directed  forward.  The 
median  plane  is  a  vertical  antero-posterior  plane,  passing  through  the  center  of  the 
trunk.  This  plane  will  pass  approximately  through  the  sagittal  suture  of  the  skull, 
and  hence  any  plane  parallel  to  it  is  termed  a  sagittal  plane.  A  vertical  plane  at 
right  angles  to  the  median  plane  passes,  roughly  speaking,  through  the  central 
part  of  the  coronal  suture  or  through  a  line  parallel  to  it;  such  a  plane  is  known  as 
a  frontal  plane  or  sometimes  as  a  coronal  plane.  A  plane  at  right  angles  to  both 
the  median  and  frontal  planes  is  termed  a  transverse  plane. 

The  terms  anterior  or  ventral,  and  posterior  or  dorsal,  are  employed  to  indicate 
the  relation  of  parts  to  the  front  or  back  of  the  body  or  limbs,  and  the  terms 
superior  or  cephalic,  and  inferior  or  caudal,  to  indicate  the  relative  levels  of  different 
structures;  structures  nearer  to  or  farther  from  the  median  plane  are  referred  to  as 
medial  or  lateral  respectively. 

The  terms  superficial  and  deep  are  strictly  confined  to  descriptions  of  the 
relative  depth  from  the  surface  of  the  various  structures;  external  and  internal 
are  reserved  almost  entirely  for  describing  the  walls  of  cavities  or  of  hollow 
viscera.  In  the  case  of  the  limbs  the  words  proximal  and  distal  refer  to  the 
relative  distance  from  the  attached  end  of  the  limb. 


EMBRYOLOGY. 


THE  term   Embryology,  in  its  widest  sense,  is  applied  to  the  various  changes 
^^  which  take  place  during  the  growth  of   an  animal  from  the  egg  to  the  adult 

^Hj  condition:  it  is,  however,  usually  restricted  to  the  phenomena  which  occur  before 
^"  birth.  Embryology  may  be  studied  from  two  aspects:  (1)  that  of  ontogeny,  which 
j^  deals  only  with  the  development  of  the  individual;  and  (2)  that  of  phylogeny, 
which  concerns  itself  with  the  evolutionary  history  of  the  animal  kingdom. 

In  vertebrate  animals  the  development  of  a  new  being  can  only  take  place  when 
a  female  germ  cell  or  ovum  has  been  fertilized  by  a  male  germ  cell  or  spermatozoon. 
The  ovum  is  a  nucleated  cell,  and  all  the  complicated  changes  by  which  the  various 
tissues  and  organs  of  the  body  are  formed  from  it,  after  it  has  been  fertilized,  are 
the  result  of  two  general  processes,  viz.,  segmentation  and  differentiation  of  cells. 
Thus,  the  fertilized  ovum  undergoes  repeated  segmentation  into  a  number  of  cells 
which  at  first  closely  resemble  one  another,  but  are,  sooner  or  later,  differentiated 
into  two  groups:  (1)  somatic  cells,  the  function  of  which  is  to  build  up  the  various 
tissues  of  the  body;  and  (2)  germinal  cells,  which  become  imbedded  in  the  sexual 
glands — the  ovaries  in  the  female  and  the  testes  in  the  male — and  are  destined  for 
the  perpetuation  of  the  species. 

Having  regard  to  the  main  purpose  of  this  work,  it  is  impossible,  in  the  space 
available  in  this  section,  to  describe  fully,  or  illustrate  adequately,  all  the  phenom- 
ena which  occur  in  the  different  stages  of  the  development  of  the  human  body. 
Only  the  principal  facts  are  given,  and  the  student  is  referred  for  further  detaUs 
to  one  or  other  of  the  text-books^  on  human  embryology. 

THE   ANIMAL   CELL. 

All  the  tissues  and  organs  of  the  body  originate  from  a  microscopic  structure 
(the  fertilized  ovum),  which  consists  of  a  soft  jelly-like  material  enclosed  in  a 
membrane  and  containing  a  vesicle  or  small  spherical  body  inside  which  are  one 
or  more  denser  spots.  This  may  be  regarded  as  a  complete  cell.  All  the  solid 
tissues  consist  largely  of  cells  essentially  similar  to  it  in  nature  but  differing  in 
external  form. 

In  the  higher  organisms  a  cell  may  be  defined  as  "a  nucleated  mass  of  proto- 
plasm of  microscopic  size."  Its  two  essentials,  therefore,  are:  a  soft  jelly-like 
material,  similar  to  that  found  in  the  ovum,  and  usually  styled  cytoplasm,  and  a 
small  spherical  body  imbedded  in  it,  and  termed  a  nucleus.  Some  of  the  unicellular 
protozoa  contain  no  nuclei  but  granular  particles  which,  like  true  nuclei,  stain  with 
basic  dyes.  The  other  constituents  of  the  ovum,  viz.,  its  limiting  membrane  and 
the  denser  spot  contained  in  the  nucleus,  called  the  nucleolus,  are  not  essential  ta 
the  type  cell,  and  in  fact  many  cells  exist  without  them. 

Csrtoplasm  (protoplas7n)  is  a  material  probably  of  variable  constitution  during 
life,  but  yielding  on  its  disintegration  bodies  chiefly  of  proteid  nature.  Lecithin 
and  cholesterin  are  constantly  found  in  it,  as  well  as  inorganic  salts,  chief  among 

1  Manual  of  Human  Embryology,  Keibel  and  Mall;  Handbuch  der  vergleichenden  und  experimentellen  Entwickel- 
ungslehre  der  Wirbeltiere,  Oskar  Hertwig;  Lehrbuch  der  Entwickelungsgeschichte,  Bonnet;  The  Physiology  of 
Reproduction,  Marshall. 

(36) 


36 


EMBRYOLOGY 


which  are  the  phosphates  and  chlorides  of  potassium,  sodium,  and  calcium.  It  is 
of  a  semifluid,  viscid  consistence,  and  probably  colloidal  in  nature.  The  living 
cjloplasm  appears  to  consist  of  a  homogeneous  and  structureless  ground-substance 
in  which  are  embedded  granules  of  ^'arious  t\'pes.  The  mitochondria  are  the  most 
constant  type  of  granule  and  vary  in  form  from  granules  to  rods  and  threads. 
Their  function  is  unknown.  Some  of  the  granules  are  proteid  in  nature  and  prob- 
ably essential  constituents;  others  are  fat,  glycogen,  or  pigment  granules,  and  are 
regarded  as  adventitious  material  taken  in  from  without,  and  hence  are  styled 
cell-inclusions  or  paraplasm.  When,  however,  cells  have  been  "fixed"  by  reagents 
a  fibrillar  or  granular  appearance  can  often  be  made  out  under  a  high  power  of  the 
microscope.  The  fibrils  are  usually  arranged  in  a  network  or  reticulum,  to  which 
the  term  spongioplasm  is  applied,  the  clear  substance  in  the  meshes  being  termed 
hyaloplasm.  The  size  and  shape  of  the  meshes  of  the  spongioplasm  vary  in  different 
cells  and  in  different  parts  of  the  same  cell.  The  relative  amounts  of  spongioplasm 
and  hyaloplasm  also  vary  in  different  cells,  the  latter  preponderating  in  the  young 
cell  and  the  former  increasing  at  the  expense  of  the  hyaloplasm  as  the  cell  grows. 
Such  appearances  in  fixed  cells  are  no  indication  whatsoever  of  the  existence  of 


Cell  wall 


NvcUar 
membrane 


Vacuole 


Centrosome  consisting  of  cen- 
trosphere  enclosing  ttvo  cen- 
trioles 

Nucleolus 

Net-knot  of  chromatin  form- 
ing a  pseudo-nucleolus 
Chromatin  network 


Cell-inclusions  {paraplasm) 


Fig.  1. — Diagram  of  a  cell.    (Modified  from  Wilson.) 


similar  structures  in  the  living,  although  there  must  have  been  something  in  the 
living  cell  to  give  rise  to  the  fixed  structures.  The  peripheral  layer  of  a  cell  is  in 
all  cases  modified,  either  by  the  formation  of  a  definite  cell  membrane  as  in  the  ovum, 
or  more  frequently  in  the  case  of  animal  cells,  by  a  transformation,  probably 
chemical  in  nature,  which  is  only  recognizable  by  the  fact  that  the  surface  of  the 
cell  behaves  as  a  semipermeable  membrane. 

Nucleus. — The  nucleus  is  a  minute  body,  imbedded  in  the  protoplasm,  and 
usually  of  a  spherical  or  oval  form,  its  size  having  little  relation  to  that  of  the  cell. 
It  is  surrounded  by  a  well-defined  wall,  the  nuclear  membrane;  this  encloses  the 
nuclear  substance  {nuclear  matrix),  which  is  composed  of  a  homogeneous  material 
in  which  is  usually  embedded  one  or  two  nucleoli.  In  fixed  cells  the  nucleus  seems 
to  consist  of  a  clear  substance  or  karyoplasm  and  a  network  or  karyomitome.  The 
former  is  probably  of  the  same  nature  as  the  hyaloplasm  of  the  cell,  but  the  latter, 
which  forms  also  the  wall  of  the  nucleus,  differs  from  the  spongioplasm  of  the  cell 
substance.  It  consists  of  fibers  or  filaments  arranged  in  a  reticular  manner.  These 
filaments  are  composed  of  a  homogeneous  material  known  as  linin,  which  stains 
with  acid  dyes  and  contains  embedded  in  its  substance  particles  which  have  a 
strong  affinity  for  basic  dyes.    These  basophil  granules  have  been  named  chromatin 


THE  ANIMAL  CELL 


37 


or  basichromatin  and  owe  their  staining  properties  to  the  presence  of  nucleic  acid. 
Within  the  nuclear  matrix  are  one  or  more  highly  refracting  bodies,  termed  nucleoli, 
connected  with  the  nuclear  membrane  by  the  nuclear  filaments.  They  are  regarded 
as  being  of  two  kinds.  Some  are  mere  local  condensations  ("net-knots")  of  the 
chromatin;  these  are  irregular  in  shape  and  are  termed  pseudo-nucleoli ;  others  are 
distinct  bodies  differing  from  the  pseudo-nucleoli  both  in  nature  and  chemical 
composition;  they  may  be  termed  true  nucleoli,  and  are  usually  found  in  resting 
cells.    The  true  nucleoli  are  oxis-phil,  i.  e.,  they  stain  with  acid  dyes. 

Most  living  cells  contain,  in  addition  to  their  protoplasm  and  nucleus,  a  small 
particle  which  usually  lies  near  the  nucleus  and  is  termed  the  centrosome.  In  the 
middle  of  the  centrosome  is  a  minute  body  called  the  centriole,  and  surrounding  this 
is  a  clear  spherical  mass  known  as  the  centrosphere.  The  protoplasm  surround- 
ing the  centrosphere  is  frequently'  arranged  in  radiating  fibrillar  rows  of  granules, 
forming  what  is  termed  the  attraction  sphere. 

Reproduction  of  Cells. — Reproduction  of  cells  is  effected  either  by  direct  or  by 
indirect  division.  In  reproduction  by  direct  division  the  nucleus  becomes  constricted 
in  its  center,  assuming  an  hour-glass  shape,  and  then  divides  into  two.  This  is  fol- 
lowed by  a  cleavage  or  division  of  the  whole  protoplasmic  mass  of  the  cell;  and  thus 
two  daughter  cells  are  formed,  each  containing  a  nucleus.  These  daughter  cells  are 
at  first  smaller  than  the  original  mother  cell;  but  they  grow,  and  the  process 
may  be  repeated  in  them,  so  that  multiplication  may  take  place  rapidly.  Indirect 
divsion  or  karyokinesis  (karyomitosis)  has  been  observed  in  all  the  tissues — genera- 
tive cells,  epithelial  tissue,  connective  tissue,  muscular  tissue,  and  nerve  tissue. 
It  is  possible  that  cell  division  may  always  take  place  by  the  indirect  method. 

The  process  of  indirect  cell  division  is  characterized  by  a  series  of  complex 
changes  in  the  nucleus,  leading  to  its  subdivision;  this  is  followed  by  cleavage 
of  the  cell  protoplasm.  Starting  with  the  nucleus  in  the  quiescent  or  resting  stage, 
these  changes  may  be  briefly  grouped  under  the  four  following  phases  (Fig.  2). 

1.  Prophase. — The  nuclear  network  of  chromatin  filaments  assumes  the  form 
of  a  twisted  skein  or  spirem,  while  the  nuclear  membrane  and  nucleolus  disappear. 
The  convoluted  skein  of  chromatin  divides  into  a  definite  number  of  V-shaped 
segments  or  chromosomes.  The  number  of  chromosomes  varies  in  different  animals, 
but  is  constant  for  all  the  cells  in  an  animal  of  any  given  species;  in  man  the  number 
is  given  by  Flemming  and  Duesberg  as  twenty-four.^  Coincidently  with  or  pre- 
ceding these  changes  the  centriole,  which  usually  lies  by  the  side  of  the  nucleus, 
undergoes  subdivision,  and  the  two  resulting  centrioles,  each  surrounded  by  a 
centrosphere,  are  seen  to  be  connected  by  a  spindle  of  delicate  achromatic  fibers 
the  achromatic  spindle.  The  centrioles  move  away  from  each  other — one  toward 
either  extremity  of  the  nucleus — and  the  fibrils  of  the  achromatic  spindle  are  cor- 
respondingly lengthened.  A  line  encircling  the  spindle  midway  between  its  ex- 
tremities or  poles  is  named  the  equator,  and  around  this  the  V-shaped  chromosomes 
arrange  themselves  in  the  form  of  a  star,  thus  constituting  the  mother  star  or 
monaster. 

2.  Metaphase.  —  Each  V-shaped  chromosome  now  undergoes  longitudinal 
cleavage  into  two  equal  parts  or  daughter  chromosomes,  the  cleavage  commencing 
at  the  apex  of  the  V  and  extending  along  its  divergent  limbs. 

3.  Anaphase. — The  daughter  chromosomes,  thus  separated,  travel  in  opposite 
directions  along  the  fibrils  of  the  achromatic  spindle  toward  the  centrioles,  around 
which  they  group  themselves,  and  thus  two  star-like  figures  are  formed,  one  at 
either  pole  of  the  achromatic  spindle.  This  constitutes  the  diaster.  The  daughter 
chromosomes  now  arrange  themselves  into  a  skein  or  spirem,  and  eventually  form 
the  network  of  chromatin  which  is  characteristic  of  the  resting  nucleus. 


Dr.  J.  Duesberg,  Anat.  Anz.,  Band  xxviii.  S.  475. 


38 


EMBRYOLOGY 


4.  Telophase. — The  cell  protoplasm  begins  to  appear  constricted  around  the 
equator  of  the  achromatic  spindle,  where  double  rows  of  granules  are  also  sometimes 
seen.  The  constriction  deepens  and  the  original  cell  gradually  becomes  divided 
into  two  new  cells,  each  with  its  own  nucleus  and  centrosome,  which  assume  the 
ordinary  positions  occupied  by  such  structures  in  the  resting  stage.  The  nuclear 
membrane  and  nucleolus  are  also  differentiated  during  this  phase. 

I      .  -,  II   .  -  """•••-. 


I 


ni 


iim  '. 


Fia.  2.— Diagram  showing  the  changes  which  occur  in  the  centrosomes  and  nucleus  of  a  cell  in  the  process  of  mitotic 
division.     (Schafer.)     /  to  ///,  prophase;  IV,  metaphase;  V  and  VI,  anaphase;  VII  and  VIII,  telophase. 


THE    OVUM. 

The  ova  are  developed  from  the  primitive  germ  cells  which  are  imbedded  in 
the  substance  of  the  ovaries.  Each  primitive  germ  cell  gives  rise,  by  repeated 
divisions,  to  a  number  of  smaller  cells  termed  oogonia,  from  which  the  ova  or 
primary  oocjrtes  are  developed. 

Human  ova  are  extremely  minute,  measuring  about  0.2  mm.  in  diameter,  and 
are  enclosed  within  the  egg  follicles  of  the  ovaries;  as  a  rule  each  follicle  contains 


THE  OVUM 


39 


single  ovum,  but  sometimes  two  or  more  are  present. "^  By  the  enlargement  and 
subsequent  rupture  of  a  follicle  at  the  surface  of  the  ovary,  an  ovum  is  liberated  and 
conveyed  by  the  uterine  tube  to  the  cavity  of  the  uterus.  Unless  it  be  fertilized 
it  undergoes  no  further  development  and  is  discharged  from  the  uterus,  but  if 
fertilization  take  place  it  is  retained  within  the  uterus  and  is  developed  into  a 
new  being. 

In  appearance  and  structure  the  ovum  (Fig.  3)  differs  little  from  an  ordinary 
cell,  but  distinctive  names  have  been  applied  to  its  several  parts;  thus,  the  cell 
substance  is  known  as  the  yolk  or  ooplasm,  the  nucleus  as  the  germinal  vesicle,  and 
the  nucleolus  as  the  germinal  spot.     The  ovum  is  enclosed  within  a  thick,  trans- 


•  3;~Human  ovum  examined  fresh  in  the  liquor  folliculi.  (Waldeyer.)  The  zona  pellucida  is  seen  as  a  thick 
clear  girdle  surrounded  by  the  cells  of  the  corona  radiata.  The  egg  itself  shows  a  central  granular  deutoplasmie  area 
and  a  peripheral  clear  layer,  and  encloses  the  germinal  vesicle,  in  which  is  seen  the  germinal  spot. 

parent  envelope,  the  zona  striata  or  zona  pellucida,  adhering  to  the  outer  surface 
of  which  are  several  layers  of  cells,  derived  from  those  of  the  follicle  and  collectively 
constituting  the  corona  radiata. 

Yolk.— The  yolk  comprises  (1)  the  cytoplasm  of  the  ordinary  animal  cell  with  its 
spongioplasm  and  hyaloplasm;  this  is  frequently  termed  the  formative  yolk;  (2) 
the  nutritive  yolk  or  deutoplasm,  which  consists  of  numerous  rounded  granules  of 
fatty  and  albuminoid  substances  imbedded  in  the  cytoplasm.  In  the  mammalian 
ovum  the  nutritive  yolk  is  extremely  small  in  amount,  and  is  of  service  in  nourish- 


See  description  of  the  ovary  on  a  future  page. 


m  ^^^B       EMBRYOLOGY  .  ^^M 

ing  the  embryo  in  the  early  stages  of  its  development  only,  whereas  in  the  egg 
of  the  bird  there  is  sufficient  to  supply  the  chick  with  nutriment  throughout 
the  whole  period  of  incubation.  The  nutritive  yolk  not  only  varies  in  amount, 
but  in  its  mode  of  distribution  within  the  egg;  thus,  in  some  animals  it  is  almost 
uniformly  distributed  throughout  the  cytoplasm;  in  some  it  is  centrally  placed  and 
is  surrounded  by  the  cytoplasm;  in  others  it  is  accumulated  at  the  lower  pole  of  the 
ovum,  while  the  cytoplasm  occupies  the  upper  pole.  A  centrosome  and  centriole 
are  present  and  lie  in  the  immediate  neighborhood  of  the  nucleus.  ■ 

Germinal  Vesicle. — The  germinal  vesicle  or  nucleus  is  a  large  spherical  body 
which  at  first  occupies  a  nearly  central  position,  but  becomes  eccentric  as  the  growth 
of  the  ovum  proceeds.  Its  structure  is  that  of  an  ordinary  cell-nucleus,  viz.,  it 
consists  of  a  reticulum  or  karyomitome,  the  meshes  of  which  are  filled  with 
karyoplasm,  while  connected  with,  or  imbedded  in,  the  reticulum  are  a  number 
of  chromatin  masses  or  chromosomes,  which  may  present  the  appearance  of  a 
skein  or  may  assume  the  form  of  rods  or  loops.  The  nucleus  is  enclosed  by  a 
delicate  nuclear  membrane,  and  contains  in  its  interior  a  well-defined  nucleolus 
or  germinal  spot. 

Coverings  of  the  Ovum. — The  zona  striata  or  zona  pellucida  (Fig.  3)  is  a  thick 
membrane,  which,  under  the  higher  powers  of  the  microscope,  is  seen  to  be  radially 
striated.  It  persists  for  some  time  after  fertilization  has  occurred,  and  may  serve 
for  protection  during  the  earlier  stages  of  segmentation.  It  is  not  yet  determined 
whether  the  zona  striata  is  a  product  of  the  cytoplasm  of  the  ovum  or  of  the  cells 
of  the  corona  radiata,  or  both. 

The  corona  radiata  (Fig.  3)  consists  or  two  or  three  strata  of  cells;  they  are 
derived  from  the  cells  of  the  follicle,  and  adhere  to  the  outer  surface  of  the  zona 
striata  when  the  ovum  is  set  free  from  the  follicle;  the  cells  are  radially  arranged 
around  the  zona,  those  of  the  innermost  layer  being  columnar  in  shape.  The 
cells  of  the  corona  radiata  soon  disappear;  in  some  animals  they  secrete,  or 
are  replaced  by,  a  layer  of  adhesive  protein,  which  may  assist  in  protecting  and 
nourishing  the  ovum. 

The  phenomena  attending  the  discharge  of  the  ova  from  the  follicles  belong 
more  to  the  ordinary  functions  of  the  ovary  than  to  the  general  subject  of  embry- 
ology, and  are  therefore  described  with  the  anatomy  of  the  ovaries.^ 

Maturation  of  the  Ovum. — Before  an  ovum  can  be  fertilized  it  must  undergo 
a  process  of  maturation  or  ripening.  This  takes  place  previous  to  or  immediately 
after  its  escape  from  the  follicle,  and  consists  essentially  of  an  unequal  subdivision 
of  the  ovum  (Fig.  4)  first  into  two  and  then  into  four  cells.  Three  of  the  four 
cells  are  small,  incapable  of  further  development,  and  are  termed  polar  bodies  or 
polocytes,  while  the  fourth  is  large,  and  constitutes  the  mature  ovum.  The  process 
of  maturation  has  not  been  observed  in  the  human  ovum,  but  has  been  carefully 
studied  in  the  ova  of  some  of  the  lower  animals,  to  which  the  following  description 
applies. 

It  was  pointed  out  on  page  37  that  the  number  of  chromosomes  found  in  the 
nucleus  is  constant  for  all  the  cells  in  an  animal  of  any  given  species,  and  that  in 
man  the  number  is  probably  twenty-four.  This  applies  not  only  to  the  somatic 
cells  but  to  the  primitive  ova  and  their  descendants.  For  the  purpose  of  illustrating 
the  process  of  maturation  a  species  may  be  taken  in  which  the  number  of  nuclear 
chromosomes  is  four  (Fig.  5) .  If  an  ovum  from  such  be  observed  at  the  beginning 
of  the  maturation  process  it  will  be  seen  that  the  number  of  its  chromosomes  is 
apparently  reduced  to  two.  In  reality,  however,  the  number  is  doubled,  since 
each  chromosome  consists  of  four  granules  grouped  to  form  a  tetrad.  During  the 
metaphase  (see  page  37)  each  tetrad  divides  into  two  dyads,  which  are  equally 


'  See  description  of  the  ovary  on  a  future  page. 


THE  OVUM 


41 


distributed  between  the  nuclei  of  the  two  cells  formed  by  the  first  division  of  the 
ovum.  One  of  the  cells  is  almost  as  large  as  the  original  ovum,  and  is  named 
the  secondary  oocyte;  the  other  is  small,  and  is  termed  the  first  polar  body.    The 


f.jm 


Fig.  4. — Formation  of  polar  bodies  in  Asterias  glacialis.  (Slightly  modified  from  Hertwig.)  In  /  the  polar  spindle 
(sp)  has  advanced  to  the  surface  of  the  egg.  In  //  a  small  elevation  (p6')  is  formed  which  receives  half  of  the  spindle. 
In  III  the  elevation  is  constricted  off,  forming  the  first  polar  body  (p6'),  and  a  second  spindle  is  formed.  In  IV  is 
seen  a  second  elevation  which  in  V  has  been  constricted  off  as  the  second  polar  body  (p6').  Out  of  the  remainder  of 
the  spindle  (/.p»  in  VI)  the  female  pronucleus  is  developed. 

secondary  oocyte  now  undergoes  subdivision,  during  which  each  dyad  divides  and 
contributes  a  single  chromosome  to  the  nucleus  of  each  of  the  two  resulting  cells. 


Priviary  oocyte 


Primary  oocyte 
(commencing 
maturation) 


(       f       ]  First  polar 
V  J       body 


Secondary 
oocyte 


Mature  f    *@      \   /^\      /*S\      /*0\ 


V^ 


WV_^ 


I 


Polar  bodies  ' 

FiQ.  5. — Diagram  showing  the  reduction  in  number  of  the  chromosomes  in  the  process  of  maturation  of  the  ovum. 

This  second  division  is  also  unequal,  producing  a  large  cell  which  constitutes  the 
mature  ovum,  and  a  small  cell,  the  second  polar  body.  The  first  polar  body  fre- 
quently divides  while  the  second  is  being  formed,  and  as  a  final  result  four  cells 


42 


EMBRYOLOGY 


are  produced,  viz.,  the  mature  ovum  and  three  polar  bodies,  each  of  which  con- 
tains two  chromosomes,  i.  e.,  one-half  the  number  present  in  the  nuclei  of  the 
somatic  cells  of  members  of  the  same  species.  The  nucleus  of  the  mature  ovum 
is  termed  the  female  pronucleus. 


THE    SPERMATOZOON. 


dl 


The  spermatozoa  or  male  germ  cells  are  developed  in  the  testes  and  are  present 
in  enormous  numbers  in  the  seminal  fluid.  Each  consists  of  a  small  but  greatly 
modified  cell.  The  human  spermatozoon  possesses  a  head,  a  neck,  a  connecting, 
piece  or  body,  and  a  tail  (Fig.  6). 


Head 


Connecting  piece 


•Perforator 


)  Neck 


Tail! 


End-piece  > 


I 


^  Head-cap 


J 


■-•A nterior  centriole 
""Posterior  centriole 


-—'Spiral  thread 

Mitochondria  sheath 


Terminal  disc 
Axial  filament 


I 


Fig.  6. — Human  spermatozoon.      Diagrammatic.      A.  Surface  view.      B.  Profile  view.      In  C  the  head,  neck, 
and  connecting  piece  are  more  highly  magnified. 

The  head  is  oval  or  elliptical,  but  flattened,  so  that  when  viewed  in  profile 
it  is  pear-shaped.  Its  anterior  two-thirds  are  covered  by  a  layer  of  modified  proto- 
plasm, which  is  named  the  head-cap.  This,  in  some  animals,  e.  g.,  the  salamander, 
is  prolonged  into  a  barbed  spear-like  process  or  perforator,  which  probably  facilitates 
the  entrance  of  the  spermatozoon  into  the  ovum.  The  posterior  part  of  the  head 
exhibits  an  affinity  for  certain  reagents,  and  presents  a  transversely  striated  appear- 
ance, being  crossed  by  three  or  four  dark  bands.  In  some  animals  a  central  rod- 
like filament  extends  forward  for  about  two-thirds  of  the  length  of  the  head,  while 
in  others  a  rounded  body  is  seen  near  its  center.    The  head  contains  a  mass  of 


THE  SPERMATOZOON 


43 


chromatin,  and  is  generally  regarded  as  the  nucleus  of  the  cell  surrounded  by  a 
thin  envelope. 

The  neck  is  less  constricted  in  the  human  spermatozoon  than  in  those  of  some 
of  the  lower  animals.  The  anterior  centriole,  represented  by  two  or  three  rounded 
particles,  is  situated  at  the  junction  of  the  head  and  neck,  and  behind  it  is  a  band 
of  homogeneous  substance. 

The  connecting  piece  or  body  is  rod-like,  and  is  limited  behind  by  a  terminal 
disk.  The  posterior  centriole  is  placed  at  the  junction  of  the  body  and  neck  and, 
like  the  anterior,  consists  of  two  or  three  rounded  particles.  From  this  centriole 
an  axial  filament,  surrounded  by  a  sheath,  runs  backward  through  the  body  and 
tail.  In  the  body  the  sheath  of  the  axial  filament  is  encircled  by  a  spiral  thread, 
around  which  is  an  envelope  containing  mitochondria  granules,  and  termed  the 
mitochondria  sheath. 

The  tail  is  of  great  length,  and  consists  of  the  axial  thread  or  filament,  sur- 
rounded by  its  sheath,  which  may  contain  a  spiral  thread  or  may  present  a  striated 
appearance.  The  terminal  portion  or  end-piece  of  the  tail  consists  of  the  axial 
filament  onlv. 


Primary  oocyte 


Primary  spermatocyte 


Secondary  (       \ 
oocyte     K      J 


Mature 


O 


O  Secondary 
spermatocytes 


Oooooo  oo 


Polar  bodies 


Spermatids 


FiQ.  7. — Scheme  showing  analogies  in  the  process  of  maturation  of  the  ovum  and  the  development  of  the  spermatids 

(young  spermatozoa). 


Krause  gives  the  length  of  the  human  spermatozoon  as  between  52 /x  and  62 /x, 
the  head  measuring  4  to  5m,  the  connecting  piece  G^t,  and  the  tail  from  41  ^i  to  52 fx. 

By  virtue  of  their  tails,  which  act  as  propellers,  the  spermatozoa  are  capable  of 
free  movement,  and  if  placed  in  favorable  surroundings,  e.  g.,  in  the  female  pas- 
sages, will  retain  their  vitality  and  power  of  fertilizing  for  several  days.  In  certain 
animals,  e.  g.,  bats,  it  has  been  proved  that  spermatozoa  retained  in  the  female 
passages  for  several  months  are  capable  of  fertilizing. 

The  spermatozoa  are  developed  from  the  primitive  germ  cells  which  have  become 
imbedded  in  the  testes,  and  the  stages  of  their  development  are  very  similar  to  those 
of  the  maturation  of  the  ovum.  The  primary  germ  cells  undergo  division  and 
produce  a  number  of  cells  termed  spermatogonia,  and  from  these  the  primary 
spermatocytes  are  derived.  Each  primary  spermatocyte  divides  into  two  secondary 
spermatocytes,  and  each  secondary  spermatocyte  into  two  spermatids  or  young 
spermatozoa;  from  this  it  will  be  seen  that  a  primary  spermatocyte  gives  rise  to 
four  spermatozoa.  On  comparing  this  process  with  that  of  the  maturation  of  the 
ovum  (Fig.  7)  it  will  be  observed  that  the  primary  spermatocyte  gives  rise  to 
two  cells,  the  secondary  spermatocytes,  and  the  primary  oocyte  to  two  cells,  the 
secondary  oocyte  and  the  first  polar  body.     Again,  the  two  secondary  sperma- 


EMBRYOR 

tocytes  by  their  subdivision  give  origin  to  four  spermatozoa,  and  the  secondary 
oocyte  and  first  polar  body  to  four  cells,  the  mature  ovum  and  three  polar  bodies. 
In  the  development  of  the  spermatozoa,  as  in  the  maturation  of  the  ovum,  there 
is  a  reduction  of  the  nuclear  chromosomes  to  one-half  of  those  present  in  the 
primary  spermatocyte.  But  here  the  similarity  ends,  for  it  must  be  noted  that 
the  four  spermatozoa  are  of  equal  size,  and  each  is  capable  of  fertilizing  a  mature 
ovum,  whereas  the  three  polar  bodies  are  not  only  very  much  smaller  than  the 
mature  ovum  but  are  incapable  of  further  development,  and  may  be  regarded  as 
abortive  ova. 


I 


FERTILIZATION    OF    THE    OVUM. 


Fertilization  consists  in  the  union  of  the  spermatozoon  with  the  mature  ovum 
(Fig.  8).    Nothing  is  known  regarding  the  fertilization  of  the  human  ovum,  but 


II 


1.     Polar  bodies- 
Female  pronucleus 

Male  pronucleus 


Female  pronudetis 
Male  pronucleus 


5. 


Segmentation 
nucleus 


Female  promtcleus 
Male  pronucleus 


~  Fused  pronuclei 


Segmentation 

nucleus 
{commencing 

division) 


Fio.  8. — The  process  of  fertilization  in  the  ovum  of  a  mouse.     (After  Sobotta.) 

the  various  stages  of  the  process  have  been  studied  in  other  mammals,  and  from 
the  knowledge  so  obtained  it  is  believed  that  fertilization  of  the  human  ovum  takes 
place  in  the  lateral  or  ampullary  part  of  the  uterine  tube,  and  the  ovum  is  then 
conveyed  along  the  tube  to  the  cavity  of  the  uterus — a  journey  probably  occupy- 
ing seven  or  eight  days  and  during  which  the  ovum  loses  its  corona  radiata  and  zona 
striata  and  undergoes  segmentation.  Sometimes  the  fertilized  ovum  is  arrested 
in  the  uterine  tube,  and  there  undergoes  development,  giving  rise  to  a  tubal  preg- 
nancy; or  it  may  fall  into  the  abdominal  cavity  and  produce  an  abdominal  preg- 
nancy. Occasionally  the  ovum  is  not  expelled  from  the  follicle  when  the  latter 
ruptures,  but  is  fertilized  within  the  follicle  and  produces  what  is  known  as  an 
ovarian  pregnancy.  Under  normal  conditions  only  one  spermatozoon  enters  the 
yolk  and  takes  part  in  the  process  of  fertilization.    At  the  point  where  the  sperma 


SEGMENTATION  OF  THE  FERTILIZED  OVUM 


45 


tozoon  is  about  to  pierce,  the  yolk  is  drawn  out  into  a  conical  elevation,  termed 
the  cone  of  attraction.  As  soon  as  the  spermatozoon  has  entered  the  yolk,  the  per- 
ipheral portion  of  the  latter  is  transformed  into  a  membrane,  the  vitelline  membrane 
which  prevents  the  passage  of  additional  spermatozoa.  Occasionally  a  second 
spermatozoon  may  enter  the  yolk,  thus  giving  rise  to  a  condition  of  polyspermy: 
when  this  occurs  the  ovum  usually  develops  in  an  abnormal  manner  and  gives  rise 
to  a  monstrosity.  Having  pierced  the  yolk,  the  spermatozoon  loses  its  tail,  while 
its  head  and  connecting  piece  assume  the  form  of  a  nucleus  containing  a  cluster  of 
chromosomes.  This  constitutes  the  male  pronucleus,  and  associated  with  it  there  are 
a  centriole  and  centrosome.  The  male  pronucleus  passes  more  deeply  into  the  yolk, 
and  coincidently  with  this  the  granules  of  the  cytoplasm  surrounding  it  become 
radially  arranged.  The  male  and  female  pronuclei  migrate  toward  each  other,  and. 
meeting  near  the  center  of  the  yolk,  fuse  to  form  a  new  nucleus,  the  segmentation 
nucleus,  which  therefore  contains  both  male  and  female  nuclear  substance;  the 
former  transmits  the  individualities  of  the  male  ancestors,  the  latter  those  of  the 
female  ancestors,  to  the  future  embryo.  By  the  union  of  the  male  and  female 
pronuclei  the  number  of  chromosomes  is  restored  to  that  which  is  present  in  the 
nuclei  of  the  somatic  cells. 


Fig.  9. — First  stages  of  segmentation  of  a  mammalian  ovum.  Semidiagrammatic.  (From  a  drawing  by  Allen 
liomson.)  z.p.  Zona  striata,  p.gl-  Polar  bodies,  a.  Twocell  stage,  h.  Four-cell  stage,  c.  Eight-cell  stage. 
t.  Morula  stage. 


SEGMENTATION   OF   THE   FERTILIZED    OVUM. 

The  early  segmentation  of  the  human  ovum  has  not  yet  been  observed,  but 
judging  from  what  is  known  to  occur  in  other  mammals  it  may  be  regarded  as 
certain  that  the  process  starts  immediately  after  the  ovum  has  been  fertilized, 
i.  e.,  while  the  ovum  is  in  the  uterine  tube.  The  segmentation  nucleus  exhibits 
the  usual  mitotic  changes,  and  these  are  succeeded  by  a  division  of  the  ovum  into 
two  cells  of  nearly  equal  size.^    The  process  is  repeated  again  and  again,  so  that 

>  In  the  mammalian  ova  the  nutritive  yolk  or  deutoplasm  is  small  in  amount  and  uniformly  distributed  through- 
out the  cytoplasm;  such  ova  undergo  complete  division  during  the  process  of  segmentation,  and  are  therefore  termed 
holoblashc.  In  the  ova  of  birds,  reptiles,  and  fishes  where  the  nutritive  volk  forms  by  far  the  larger  portion  of  the 
^K^k'  t  '^'^^^'i^Se  IS  limited  to  the  formative  yolk,  and  is  therefore  only  partial;  such  ova  are  termed  meroblastic.  Again, 
It  has  been  observed,  in  some  of  the  lower  animals,  that  the  pronuclei  do  not  fuse  but  merely  lie  in  apposition.  At 
the  commencement  of  the  segmentation  process  the  chromosomes  of  the  two  pronuclei  group  themselves  around  the 
equator  of  the  nuclear  spindle  and  then  divide ;  .in  equal  number  of  male  and  female  chromosomes  travel  to  the  opposite 
poles  of  the  spindle,  and  thus  the  male  and  female  pronuclei  contribute  equal  shares  of  chromatin  to  the  nuclei  of 
the  two  cells  which  result  from  the  subdivision  of  the  fertilized  ovum 


46 


EMBRYOLOGY 


the  two  cells  are  succeeded  by  four,  eight,  sixteen,  thirty-two,  and  so  on,  with  the 
result  that  a  mass  of  cells  is  found  within  the  zona  striata,  and  to  this  mass  the  term 
morula  is  applied  (Fig.  9).  The  segmentation  of  the  mammalian  ovum  may  not 
take  place  in  the  regular  sequence  of  two,  four,  eight,  etc.,  since  one  of  the  two  first 
formed  cells  may  subdivide  more  rapidly  than  the  other,  giving  rise  to  a  three- 
or  a  five-cell  stage.  The  cells  of  the  morula  are  at  first  closely  aggregated,  but  soon 
they  become  arranged  into  an  outer  or  peripheral  layer,  the  trophoblast,  which 


Inner  cell-mass 

Entoderm 


Blastodermic  vesicle 


Trophoblast 


Fig.   10. — Blastodermic  vesicle  of  Vespertilio  miirinus.     (After  van  Beneden. 

Inner  cell-mass      TrofhMast 


Embryonic  ectoderm        Entoderm 
Fig.   11. — Section  through  embryonic  disk  of  Vespertilio  murinus.     (After  van  Beneden.) 


#1 


Maternal  bloodvessels 


Amniotic  cavity 


Syncytiotrcphoblast 

CyMrcpTioblast 


Embryonic  ectoderm      Entoderm 

Fig.   12. — Section  through  embryonic  area  of  Vespertilio  murinus  to  show  the  formation  of  the  amniotic  cavity. 

(After  van  Beneden,) 

does  not  contribute  to  the  formation  of  the  embryo  proper,  and  an  inner  cell-mass, 
from  which  the  embryo  is  developed.  Fluid  collects  between  the  trophoblast 
and  the  greater  part  of  the  inner  cell-mass,  and  thus  the  morula  is  converted  into 
a  vesicle,  the  blastodermic  vesicle  (Fig.  10).  The  inner  cell-mass  remains  in  con- 
tact, however,  with  the  trophoblast  at  one  pole  of  the  ovum;  this  is  named  the 
embryonic  pole,  since  it  indicates  the  situation  where  the  future  embryo  will  be 
developed.    The  cells  of  thf.  trophoblast  become  differentiated  into  two  strata:  an 


SEGMENTATION  OF  THE  FERTILIZED  OVUM 


47 


I   outer,  termed  the  syncytium  or  s3mcytiotrophoblast,  so  named  because  it  consists  of 
j  a  layer  of  protoplasm  studded  with  nuclei,  but  showing  no  evidence  of  subdivision 
into  cells;  and  an  inner  layer,  the  cytotrophoblast  or  layer  of  Langhans,  in  which 
the  cell  outlines  are  defined.    As  already  stated,  the  cells  of  the  trophoblast  do  not 
contribute  to  the  formation  of  the  embryo  proper;  they  form  the  ectoderm  of  the 
chorion  and  play  an  important  part  in  the  development  of  the  placenta.    On  the 
deep  surface  of  the  inner  cell-mass  a  layer  of  flattened  cells,  the  entoderm,  is  differ- 
entiated and  quickly  assumes  the  form  of  a  small  sac,  the  yolk-sac.    Spaces  appear 
between  the  remaining  cells  of  the  mass  (Fig.  11),  and  by  the  enlargement  and 
coalescence  of  these  spaces  a  cavity,  termed  the  amniotic  cavity  (Fig.  12),  is  gradually 
^^    developed.    The  floor  of  this  cavity  is  formed  by  the  embryonic  disk  composed 
^■1  of  a  layer  of  prismatic  cells,  the  embryonic  ectoderm,  derived  from  the  inner  cell- 
^H  mass  and  lying  in  apposition  with  the  entoderm. 

^■1      The  Primitive  Streak;  Formation  of  the  Mesoderm. — The  embryonic   disk 
^H  becomes  oval  and  then  pear-shaped,  the  wider  end  being  directed  forward.    Near 
!■'  the  narrow,  posterior  end  an  opaque  streak,  the  primitive 
streak  (Figs.  13  and  14),  makes  its  appearance  and  extends 
along  the  middle  of  the  disk  for  about  one-half  of  its 
length;  at  the  anterior  end  of  the  streak  there  is  a  knob- 
like thickening  termed  Hensen's  knot.     A  shallow  groove, 
the  primitive  groove,  appears  on  the  surface  of  the  streak, 
and   the  anterior  end  of  this  groove  communicates  by 
means  of  an  aperture,  the  blastophore,  with  the  yolk-sac. 
The  primitive  streak  is  produced  by  a  thickening  of  the 
axial  part  of  the  ectoderm,  the  cells  of  which  multiply, 
grow  downward,  and   blend  with  those  of  the  subjacent 
entoderm  (Fig.  15).    From  the  sides  of  the  primitive  streak 
a  third  layer  of  cells,  the  mesoderm,  extends  lateralward 
I         between  the  ectoderm  and  entoderm;  the  caudal  end  of 
Hi  the  primitive  streak  forms  the  cloacal  membrane. 
"  ■       The  extension  of  the  mesoderm  takes  place  throughout  the  whole  of  the  embry- 
onic and  extra-embryonic  areas  of  the  ovum,  except  in  certain  regions.    One  of 
these  is  seen  immediately  in  front  of  the  neural  tube.    Here  the  mesoderm  extends 
»        forward  in  the  form  of  two  crescentic  masses,  which  meet  in  the  middle  line  so  as 
Hi  to  enclose  behind  them  an  area  which  is  devoid  of  mesoderm.    Over  this  area  the 
r     ectoderm  and  entoderm  come  into  direct  contact  with  each  other  and  constitute 
a  thin  membrane,  the  buccopharyngeal  membrane,  which  forms  a  septum  between 
the  primitive  mouth  and  pharynx.    In  front  of  the  buccopharyngeal  area,  where 
the  lateral  crescents  of  mesoderm  fuse  in  the  middle  line,  the  pericardium  is 
afterward  developed,  and  this  region  is  therefore  designated  the  pericardial  area.    A 
second  region  where  the  mesoderm  is  absent,  at  least  for  a  time,  is  that  imme- 
diately in  front  of  the  pericardial  area.    This  is  termed  the  proamniotic  area,  and 
is  the  region  where  the  proamnion  is  developed;  in  man,  however,  a  proamnion  is 
apparently  never  formed.     A  third  region  is  at  the  hind  end  of  the  embryo  where 
the  ectoderm  and  entoderm  come  into  apposition  and  form  the  cloacal  membrane. 
The  blastoderm  now  consists  of  three  layers,  named  from  without  inward: 
ectoderm,  mesoderm,  and  entoderm;  each  has  distinctive  characteristics  and  gives 
rise  to  certain  tissues  of  the  body.^ 

Ectoderm. — ^The  ectoderm  consists  of  columnar  cells,  which  are,  however,  somewhat 
flattened  or  cubical  toward  the  margin  of  the  embryonic  disk.  It  forms  the  whole 
of  the  nervous  system,  the  epidermis  of  the  skin,  the  lining  cells  of  the  sebaceous, 


Fig.  13. — Surface  view  of 
embryo  of  a  rabbit.  (After 
KoUiker.)  arg.  Embryonic 
disk.     pr.  Primiti%'e  streak. 


I 


'  The  mode  of  formation  of  the  germ  layers  in  the  human  ovum  has  not  yet  been  observed;  in  the  youngest  known 
human  ovum  (viz.,  that  described  by  Bryce  and  Teacher),  all  three  layers  are  already  present  and  the  mesoderm  is 
split  into  its  two  layers.  The  extra-embryonic  celom  is  of  considerable  size,  and  scattered  mesodermal  strands  are 
seen  stretching  between  the  mesoderm  of  the  yolk-sac  and  that  of  the  chorion. 


Amnion 


Allantois  in  body-stalk 


EMBRYO! 

Yolk-sac 


- — Y  }         Notochord 


Amnion 


-f — -gf •  Neurenteric  canal 

Primitive  streak 


'     Fig.   14. — Surface  view  of  embrj'o  of  Hylobates  concolor.    (After  Selenka.)    The  amnion  has  been  opened  to  expose 

the  embryonic  disk. 


m 


HI 


Fig.  15. — Series  of  transverse  sections  through  the  embryonic  disk  of  Tarsius.  (After  Hubrecht )  Section  /  passes 
through  the  disk,  in  front  of  Hensen's  knot  and  shows  only  the  ectoderm  and  entoderm.  Sections  //,  III,  and  IV  pass 
through  Hensen's  knot,  which  is  seen  in  V  tapering  away  into  the  primitive  streak.  In  III,  IV,  and  V  the  mesoderm 
is  seen  springing  from  the  keel-like  thickening  of  the  ectoderm,  which  in  III  and  IV  is  observed  to  be  continuous  into 
the  entoderm. 


SEGMENTATION  OF  THE  FERTILIZED  OVUM 


49 


sudoriferous-,  and  mammary  glands,  the  hairs  and  nails,  the  epithelium  of  the  nose 
and  adjacent  air  sinuses,  and  that  of  the  cheeks  and  roof  of  the  mouth.  From  it 
also  are  derived  the  enamel  of  the  teeth,  and  the  anterior  lobe  of  the  hypophysis 
cerebri,  the  epithelium  of  the  cornea,  conjunctiva,  and  lacrimal  glands,  and  the 
neuro-epithelium  of  the  sense  organs. 

Entoderm. — The  entoderm  consists  at  first  of  flattened  cells,  which  subsequently 

become  columnar.    It  forms  the  epithelial  lining  of  the  whole  of  the  digestive  tube 

excepting  part  of  the  mouth  and  pharynx  and  the  terminal  part  of  the  rectum 

(which  are  lined  by  involutions  of  the  ectoderm),  the  lining  cells  of  all  the  glands 

I,    which  open  into  the  digestive  tube,  including  those  of  the  liver  and  pancreas, 


HL 


IV.    ^ 


8m 
sp 


Fig.  16. — A  series  of  transverse  sections  through  an  embryo  of  the  dog.  (After  Bonnet.)  Section  I  is  the  most 
anterior.  In  V  the  neural  plate  is  spread  out  nearly  flat.  The  series  shows  the  uprising  of  the  neural  folds  to  form  the 
neural  canal,  a.  Aortse.  c.  Intermediate  cell  mass.  ect.  Ectoderm,  ent.  Entocferm.  h,  h.  Rudiments  of  endothelial 
heart  tubes.  In  ///,  IV,  and  V  the  scattered  cells  represented  between  the  entoderm  and  splanchnic  layer  of  meso- 
derm are  the  vasoformative  cells  which  give  origin  in  front,  according  to  Bonnet,  to  the  heart  tubes,  h;  l.p.  Lateral 
plate  still  undivided  in  7,  II,  and  III;  in  IV  and  V  split  into  somatic  (sm)  and  splanchnic  (sp)  layers  of  mesoderm. 
mea.  Mesoderm,     p.  Pericardium,     so.  Primitive  segment. 

the  epithelium  of  the  auditory  tube  and  tympanic  cavity,  of  the  trachea,  bronchi, 
and  air  cells  of  the  lungs,  of  the  urinary  bladder  and  part  of  the  urethra,  and  that 
which  lines  the  follicles  of  the  thyroid  gland  and  thymus. 

Mesoderm. — ^The  mesoderm  consists  of  loosely  arranged  branched  cells  sur- 
rounded by  a  considerable  amount  of  intercellular  fluid.  From  it  the  remaining 
tissues  of  the  body  are  developed.  The  endothelial  lining  of  the  heart  and  blood- 
vessels and  the  blood  corpuscles  are,  however,  regarded  by  some  as  being  of  ento- 
dermal  origin. 

As  the  mesoderm  develops  between  the  ectoderm  and  entoderm  it  is  separated 
into  lateral  halves  by  the  neural  tube  and  notochord,  presently  to  be  described.  A 
4 


50 


EMBRYOLOGY 


I 


longitudinal  groove  appears  on  the  dorsal  surface  of  either  half  and  divides  it  into 
a  medial  column,  the  paraxial  mesoderm,  lying  on  the  side  of  the  neural  tube,  and 
a  lateral  portion,  the  lateral  mesoderm.  The  mesoderm  in  the  floor  of  the  groove 
connects  the  paraxial  with  the  lateral  mesoderm  and  is  known  as  the  intermediate 
cell-mass;  in  it  the  genito-urinary  organs  are  developed.  The  lateral  mesoderm 
splits  into  two  layers,  an  outer  or  somatic,  which  becomes  applied  to  the  inner  surface 
of  the  ectoderm,  and  with  it  forms  the  somatopleure ;  and  an  inner  or  splanchnic, 
which  adheres  to  the  entoderm,  and  with  it  forms  the  splanchnoplem-e  (Fig.  IG). 
The  space  between  the  two  layers  of  the  lateral   mesoderm  is  termed  the  celom. 

THE  NEURAL  GROOVE  AND  TUBE.  ^1 

In  front  of  the  primitive  streak  two  longitudinal  ridges,  caused  by  a  folding  up 
of  the  ectoderm,  make  their  appearance,  one  on  either  side  of  the  middle  line 
(Fig.  16).    These  are  named  the  neural  folds;  they  commence  some  little  distance 


Ydksac 


Amnion 


Neural  groove 


Neurenteric  canal 

Primitive  streak 
Body-stalk 


f  IG.    17. — Human  embryo — length,  2  mm.     Dorsal  view,  with  the  amnion  laid  open.     X  30.     (After  Graf  Spee.)  ' 


behind  the  anterior  end  of  the  embryonic  disk,  where  they  are  continuous  with 
each  other,  and  from  there  gradually  extend  backward,  one  on  either  side  of  the 
anterior  end  of  the  primitive  streak.  Between  these  folds  is  a  shallow  median 
groove,  the  neural  groove  (Figs.  16, 17) .  The  groove  gradually  deepens  as  the  neural 
folds  become  elevated,  and  ultimately  the  folds  meet  and  coalesce  in  the  middle  line 
and  convert  the  groove  into  a  closed  tube,  the  neural  tube  or  canal  (Fig.  18),  the 
ectodermal  wall  of  which  forrns  the  rudiment  of  the  nervous  system.  After  the 
coalescence  of  the  neural  folds  over  the  anterior  end  of  the  primitive  streak,  the 
blastopore  no  longer  opens  on  the  surface  but  into  the  closed  canal  of  the  neural 
tube,  and  thus  a  transitory  communication,  the  neurenteric  canal,  is  established 
between  the  neural  tube  and  the  primitive  digestive  tube.  The  coalescence  of  the 
neural  folds  occurs  first  in  the  region  of  the  hind-brain,  and  from  there  extends 
forward  and  backward;  toward  the  end  of  the  third  week  the  front  opening  (anterior 
neuropore)  of  the  tube  finally  closes  at  the  anterior  end  of  the  future  brain,  and 
forms  a  recess  which  is  in  contact,  for  a  time,  with  the  overlying  ectoderm;  the 
hinder  part  of  the  neural  groove  presents  for  a  time  a  rhomboidal  shape,  and  to  this 


THE  NEURAL  GROOVE  AND  TUBE 


51 


expanded  portion  the  term  sinus  rhomboidalis  has  been  applied  (Fig.  18).  Before 
the  neural  groove  is  closed  a  ridge  of  ectodermal  cells  appears  along  the  prominent 
margin  of  each  neural  fold ;  this  is  termed  the  neural  crest  or  ganglion  ridge,  and  from 
it  the  spinal  and  cranial  nerve  ganglia  and  the  ganglia  of  the  sympathetic  nervous 
system  are  developed.  By  the  upward  growth  of  the  mesoderm  the  neural  tube 
is  ultimately  separated  from  the  overlying  ectoderm. 


.Head  fold  of  amnion  partly 
covering  the  fore-brain 


Mid-brain  -' 


Hind-brain 


Nerve  ganglion 
Auditory  vesicle 


Vitelline  vein 


Fourteenth  'primitive  -7 
segment 


Paraxial  mesoderm  -%_ 
Neural  fold 


f 


Sinus  rhomboidalis  - 


Htnvains  of  primitive  streak  - 


Heart 


Fig.   18. — Chick  embryo  of  thirty-thi' 

(From  Dm 


ion,  viewed  from  the  dorsal  aspect.     X  30. 
u  Embrj'ologie.") 


The  cephalic  end  of  the  neural  groove  exhibits  several  dilatations,  which,  when 
the  tube  is  closed,  assume  the  form  of  three  vesicles;  these  constitute  the  three 
primary  cerebral  vesicles,  and  correspond  respectively  to  the  future  fore-brain  (pros- 
encephalon), mid-brain  (mesencephalon),  and  hind-brain  (rhombencephalon)  (Fig. 
18).  The  walls  of  the  vesicles  are  developed  into  the  nervous  tissue  and  neuroglia 
of  the  brain,  and  their  cavities  are  modified  to  form  its  ventricles.    The  remainder 


IBRYOLOGY 


I 


of  the  tube  forms  the  medulla  spinalis  or  spinal  cord;  from  its  ectodermal  wall 
the  nervous  and  neuroglial  elements  of  the  medulla  spinalis  are  developed  while 
the  cavity  persists  as  the  central  canal. 


THE  NOTOCHORD.  '■ 

The  notochord  (Fig.  19)  consists  of  a  rod  of  cells  situated  on  the  ventral  aspect 
of  the  neural  tube ;  it  constitutes  the  foundation  of  the  axial  skeleton,  since  around 
it  the  segments  of  the  vertebral  column  are  formed.  Its  appearance  synchronizes 
with  that  of  the  neural  tube.  On  the  ventral  aspect  of  the  neural  groove  an  axial 
thickening  of  the  entoderm  takes  place;  this  thickening  assumes  the  appearance 
of  a  furrow — the  chordal  furrow — the  margins  of  which  come  into  contact,  and  so 
convert  it  into  a  solid  rod  of  cells — the  notochord — which  is  then  separated  from 
the  entoderm.     It  extends  throughout  the  entire  length  of  the  future  vertebral 


Ectoderm  .. 


Neural  canal  Primitive    Wolffian 

segment    duct  Celom 


Somatic  mesoderm 


Entoderm  >'  _ 

Notochord  Aorta      Splanchnic  mesoderm 

Fig.   19. — Transverse  section  of  a  chick  embryo  of  forty-five  hours'  incubation. 


(Balfour.) 


column,  and  reaches  as  far  as  the  anterior  end  of  the  mid-brain,  where  it  ends  in 
a  hook-like  extremity  in  the  region  of  the  future  dorsum  sellse  of  the  sphenoid 
bone.  It  lies  at  first  between  the  neural  tube  and  the  entoderm  of  the  yolk-sac, 
but  soon  becomes  separated  from  them  by  the  mesoderm,  which  grows  medial- 
ward  and  surrounds  it.  From  the  mesoderm 
surrounding  the  neural  tube  and  notochord, 
the  skull  and  vertebral  column,  and  the 
membranes  of  the  brain  and  medulla  spinalis 
are  developed. 

THE   PRIMITIVE    SEGMENTS. 


Toward  the  end  of  the  second  week 
transverse  segmentation  of  the  paraxial 
mesoderm  begins,  and  it  is  converted  into 
a  series  of  well-defined,  more  or  less  cubical 
masses,  the  primitive  segments  (Figs.  18, 
19,  20),  which  occupy  the  entire  length  of 
the  trunk  on  either  side  of  the  middle  line 
from  the  occipital  region  of  the  head.  Each 
segment  contains  a  central  cavity — myocoel 
— which,  however,  is  soon  filled  with  angular 
and  spindle-shaped  cells. 

Thef  primitive  segments  lie  immediately 
under  the  ectoderm  on  the  lateral  aspect  of 
the  neural  tube  and  notochord,  and  are  con- 
nected to  the  lateral  mesoderm  by  the  inter- 
mediate cell-mass.     Those  of  the  trunk  may 


Yolk: 


Cut  edge  of  amnion 
Primitive  segments 


FlQ. 


Neural  folds 


Neurenteric  canal 


20. — Dorsum  of  human  embryo,  2.11  mm.  in 
length.       (.\fter  Eternod.) 


SEPARATION  OF  THE  EMBRYO 


53 


f 


be  arranged  in  the  following  groups,  viz. :  cervical  8,  thoracic  12,  lumbar  5, 
sacral  5,  and  coccygeal  from  5  to  8.  Those  of  the  occipital  region  of  the  head 
are  usually  described  as  being  four  in  number.  In  mammals  primitive  segments 
of  the  head  can  be  recognized  only  in  the  occipital  region,  but  a  study  of  the 
lower  vertebrates  leads  to  the  belief  that  they  are  present  also  in  the  anterior 
part  of  the  head,  and  that  altogether  nine  segments  are  represented  in  the 
cephalic  region. 

SEPARATION    OF    THE   EMBRYO. 

The  embryo  increases  rapidly  in  size,  but  the  circumference  of  the  embryonic 
disk,  or  line  of  meeting  of  the  embryonic  and  amniotic  parts  of  the  ectoderm,  is  of 
relatively  slow  growth  and  gradually  comes  to  form  a  constriction  between  the 
embryo  and  the  greater  part  of  the  yolk-sac.  By  means  of  this  constriction,  which 
corresponds  to  the  future  umbilicus,  a  small  part  of  the  yolk-sac  is  enclosed  within 
the  embryo  and  constitutes  the  primitive  digestive  tube. 


Villi  of  chorion 


Amnion 
Embryonic  disk 


Rudiment  of  heart 


Chorion 

Mesoderm. 

Body-stalk 
Primitive  streak 


Mesoderm 


Bloodvessel 


Fia.  21. — Section  through  the  embryo  which  is  represented  in  Fig.  17.     (After  Graf  Spee.) 


The  embryo  increases  more  rapidly  in  length  than  in  width,  and  its  cephalic  and 
caudal  ends  soon  extend  beyond  the  corresponding  parts  of  the  circumference  of 
the  embryonic  disk  and  are  bent  in  a  ventral  direction  to  form  the  cephalic  and 
caudal  folds  respectively  (Figs.  26  and  27).  The  cephalic  fold  is  first  formed,  and 
as  the  proamniotic  area  (page  47)  lying  immediately  in  front  of  the  pericardial 
area  (page  47)  forms  the  anterior  limit  of  the  circumference  of  the  embryonic 
disk,  the  forward  growth  of  the  head  necessarily  carries  with  it  the  posterior  end 
of  the  pericardial  area,  so  that  this  area  and  the  buccopharyngeal  membrane  are 
folded  back  under  the  head  of  the  embryo  which  now  encloses  a  diverticulum  of  the 
yolk-sac  named  the  fore-gut.  The  caudal  end  of  the  embryo  is  at  first  connected 
to  the  chorion  by  a  band  of  mesoderm  called  the  body-stalk,  but  with  the  formation 
of  the  caudal  fold  the  body-stalk  assumes  a  ventral  position;  a  diverticulum  of  the 
\'olk-sac  extends  into  the  tail  fold  and  is  termed  the  hind-gut.     Between  the  fore-gut 


EMBRYOLOGY 

and  the  hind-gut  there  exists  for  a  time  a  wide  opening  into  the  yolk-sac,  but  the-i 
latter  is  gradually  reduced  to  a  small  pear-shaped  sac  (sometimes  termed  the) 
umbilical  vesicle),  and  the  channel  of  communication  is  at  the  same  time  narrowed ^ 
and  elongated  to  form  a  tube  called  the  vitelline  duct. 

THE   YOLK-SAC. 

The  yolk-sac  (Figs.  22  and  23)  is  situated  on  the  ventral  aspect  of  the  embryo;  i 
it  is  lined  by  entoderm,  outside  of  which  is  a  layer  of  mesoderm.  It  is  filled  with 
fluid,  the  vitelline  fluid,  which  possibly  may  be  utilized  for  the  nourishment  of  the 
embryo  during  the  earlier  stages  of  its  existence.  Blood  is  conveyed  to  the  wall  of 
the  sac  by  the  primitive  aortse,  and  after  circulating  through  a  wide-meshed  capil- 
lary plexus,  is  returned  by  the  vitelline  veins  to  the  tubular  heart  of  the  embryo. 
This  constitutes  the  vitelline  circulation,  and  by  means  of  it  nutritive  material  is 
absorbed  from  the  yolk-sac  and  conveyed  to  the  embryo.  At  the  end  of  the  fourth 
week  the  yolk-sac  presents  the  appearance  of  a  small  pear-shaped  vesicle  (umbilical 
vesicle)  opening  into  the  digestive  tube  by  a  long  narrow  tube,  the  vitelline  duct. 
The  vesicle  can  be  seen  in  the  after-birth  as  a  small,  somewhat  oval-shaped  body 


Amnion 

Heart  Yolk-sac 


Heart 


HTjoid  arch 
Mandibular  arch- 
Maxillary  process 
Eye 


Fore-limb 


Body-stalk 

Fig.  22. — Human  embryo  of  2.6  mm. 


(His.) 


Fig.  23. 


Hind-limb 


-Human  embryo  from  thirty-one  to  thirty-four 
days.      (His.) 


whose  diameter  varies  from  1  mm.  to  5  mm.;  it  is  situated  between  the  amnion 
and  the  chorion  and  may  lie  on  or  at  a  varying  distance  from  the  placenta.  As 
a  rule  the  duct  undergoes  complete  obliteration  during  the  seventh  week,  but 
in  about  three  per  cent,  of  cases  its  proximal  part  persists  as  a  diverticulum 
from  the  small  intestine,  Meckel's  diverticulum,  which  is  situated  about  three  or 
four  feet  above  the  ileocolic  junction,  and  may  be  attached  by  a  fibrous  cord  to 
the  abdominal  wall  at  the  umbilicus.  Sometimes  a  narrowing  of  the  lumen  of  the 
ileum  is  seen  opposite  the  site  of  attachment  of  the  duct. 


DEVELOPMENT   OF   THE   FETAL  MEMBRANES    AND    THE   PLACENTA. 

The  Allantois  (Figs.  25  to  28). — The  allantois  arises  as  a  tubular  diverticulum 
of  the  posterior  part  of  the  yolk-sac;  when  the  hind-gut  is  developed  the  allantois 
is  carried  backward  with  it  and  then  opens  into  the  cloaca  or  terminal  part  of  the 
hind-gut:  it  grows  out  into  the  body-stalk,  a  mass  of  mesoderm  which  lies  below 
and  around  the  tail  end  of  the  embryo.  The  diverticulum  is  lined  by  entoderm 
and  covered  by  mesoderm,  and  in  the  latter  are  carried  the  allantoic  or  umbilical 
vessels. 


)EVELOPMENT  OF  THE  FETAL  MEMBRANES  AXD  THE  PLACENTA     55 


In  reptiles,  birds,  and  many  mammals  the  allantois  becomes  expanded  into  d, 
"vesicle  which  projects  into  the  extra-embryonic  celom.  If  its  further  development 
be  traced  in  the  bird,  it  is  seen  to  project  to  the  right  side  of  the  embryo,  and, 
gradually  expanding,  it  spreads  over  its  dorsal  surface  as  a  flattened  sac  between 
the  amnion  and  the  serosa,  and  extending  in  all  directions,  ultimately  surrounds 
the  yolk.  Its  outer  wall  becomes  applied  to  and  fuses  with  the  serosa,  which  lies 
immediately  inside  the  shell  membrane.    Blood  is  carried  to  the  allantoic  sac  by 


Amniotic  cavity 


FlQ. 


Amniotic  cavity 
Yolk-sac 

Chorion 


2i. — Diagram  showing  earliest  observed  stage 
of  human  ovum. 


FlQ 


Body-stalk 
Allantois 

Yolk-sac 


-  Chorion 


25. — Diagram    illustrating    early    formation 
allantois  and  dififerentiation  of  body-stalk. 


the  two  allantoic  or  umbilical  arteries,  which  are  continuous  with  the  primitive 
aortse,  and  after  circulating  through  the  allantoic  capillaries,  is  returned  to  the 
primitive  heart  by  the  two  umbilical  veins.  In  this  way  the  allantoic  circulation, 
which  is  of  the  utmost  importance  in  connection  with  the  respiration  and  nutrition 
of  the  chick,  is  established.  Oxygen  is  taken  from,  and  carbonic  acid  is  given  up 
to  the  atmosphere  through  the  egg-shell,  while  nutritive  materials  are  at  the  same 
time  absorbed  by  the  blood  from  the  yolk. 


Amniotic  cavity 
Embryo 

Body-stalk 


Placental 
villi 


Placental 
villi 


Allantois 


Yolk-sac 


Chorion 


Body-stalk 

Allantois 
Yolk-sac 

Heart 


Heart 


Fig.  26  — Diagram  showing  later  stage  of  allan- 
toic development  with  commencing  constriction 
of  the  yolk-sac. 


Fore-gut 
Embryo 
Amniotic  cavity 

Fio.  27. — Diagram  showing  the  expansion  of  amnion 
and  delimitation  of  the  umbilicus. 


In  man  and  other  primates  the  nature  of  the  allantois  is  entirely  different  from 
that  just  described.  Here  it  exists  merely  as  a  narrow,  tubular  diverticulum  of  the 
hind-gut,  and  never  assumes  the  form  of  a  vesicle  outside  the  embryo.  With  the 
formation  of  the  amnion  the  embryo  is,  in  most  animals,  entirely  separated  from 
the  chorion,  and  is  only  again  united  to  it  when  the  allantoic  mesoderm  spreads 
over  and  becomes  applied  to  its  inner  surface.  The  human  embryo,  on  the  other 
hand,  as  was  pointed  out  by  His,  is  never  wholly  separated  from  the  chorion,  its 


56 


EMBRYOLOGY 


tail  end  being  from  the  first  connected  with  the  chorion  by  means  of  a  thick  bana 
of  mesoderm,  named  the  body-stalk  (Bauchstiel) ;  into  this  stalk  the  tube  of  th(! 
allantois  extends  (Fig.  21). 

The  Amnion. — The  amnion  is  a  membranous  sac  which  surrounds  and  protects 
the  embryo.  It  is  developed  in  reptiles,  birds,  and  mammals,  which  are  hence 
called  "Amniota;"  but  not  in  amphibia  and  fishes,  which  are  consequently  termed 
"Anamnia." 

In  the  human  embryo  the  earliest  stages  of  the  formation  of  the  amnion  have  not 
been  observed;  in  the  youngest  embryo  which  has  been  studied  the  amnion  was 
already  present  as  a  closed  sac  (Figs.  24  and  32),  and,  as  indicated  on  page  46, 
appears  in  the  inner  cell-mass  as  a  cavity.  This  cavity  is  roofed  in  by  a  single 
stratum  of  flattened,  ectodermal  cells,  the  amniotic  ectoderm,  and  its  floor  consists 
of  the  prismatic  ectoderm  of  the  embryonic  disk — the  continuity  between  the 

roof  and  floor  being  established  at 
the  margin  of  the  embryonic  disk. 
Outside  the  amniotic  ectoderm  is 
a  thin  layer  of  mesoderm,  which 
continuous   with    that   of    the 


Placental  villi 


IS 


Yolk-sac 


Umbilical  cord 

Allantois 
Heart 
Digestive  tvbe 


Embryo 
Amniotic  cavity 

Fio.  28. — Diagram  illustrating  a  later  stage  in  the  development 
of  the  umbilical  cord. 


somatopleure  and  is  connected  by 
the  body-stalk  with  the  meso- 
dermal lining  of  the  chorion. 

When  first  formed  the  amnion 
is  in  contact  with  the  body  of  the 
embryo,  but  about  the  fourth  or 
fifth  week  fluid  {liquor  amnii)  be- 
gins to  accumulate  within  it.  This 
fluid  increases  in  quantity  and 
causes  the  amnion  to  expand  and 
ultimately  to  adhere  to  the  inner 
surface  of  the  chorion,  so  that  the 
extra-embryonic  part  of  the  celom 
is  obliterated.  The  liquor  amnii 
increases  in  quantity  up  to  the 
sixth  or  seventh  month  of  preg- 
nancy, after  which  it  diminishes 
somewhat;  at  the  end  of  preg- 
nancy it  amounts  to  about  1  liter.  It  allows  of  the  free  movements  of  the  fetus 
during  the  later  stages  of  pregnancy,  and  also  protects  it  by  diminishing  the  risk 
of  injury  from  without.  It  contains  less  than  2  per  cent,  of  solids,  consisting  of 
urea  and  other  extractives,  inorganic  salts,  a  small  amount  of  protein,  and  frequently 
a  trace  of  sugar.  That  some  of  the  liquor  amnii  is  swallowed  by  the  fetus  is  proved 
by  the  fact  that  epidermal  debris  and  hairs  have  been  found  among  the  contents  of 
the  fetal  alimentary  canal. 

In  reptiles,  birds,  and  many  mammals  the  amnion  is  developed  in  the  following 
manner:  At  the  point  of  constriction  where  the  primitive  digestive  tube  of  the 
embryo  joins  the  yolk-sac  a  reflection  or  folding  upward  of  the  somatopleure  takes 
place.  This,  the  amniotic  fold  (Fig.  29),  first  makes  its  appearance  at  the  cephalic 
extremity,  and  subsequently  at  the  caudal  end  and  sides  of  the  embryo,  and  grad- 
ually rising  more  and  more,  its  different  parts  meet  and  fuse  over  the  dorsal  aspect 
of  the  embryo,  and  enclose  a  cavity,  the  amniotic  cavity.  After  the  fusion  of  the 
edges  of  the  amniotic  fold,  the  two  layers  of  the  fold  become  completely  separated, 
the  inner  forming  the  amnion,  the  outer  the  false  anmion  or  serosa.  The  space 
between  the  amnion  and  the  serosa  constitutes  the  extra-embryonic  celom,  and 
for  a  time  communicates  with  the  embryonic  celom. 


I 


DEVELOPMENT  OF  THE  FETAL  MEMBRANES  AND  THE  PLACENTA     57 


The  Umbilical  Cord  and  Body-stalk. — ^The  umbilical  cord  (Fig.  28)  attaches 
the  fetus  to  the  placenta;  its  length  at  full  time,  as  a  rule,  is  about  equal  to  the 


Fig.  29. — Diagram  of  a  transverse  section,  showing  the  mode  of  formation  of  the  amnion  in  the  chick.  The  amniotic 
folds  have  nearly  united  in  the  middle  line.  (From  Quain's  Anatomy.)  Ectoderm,  blue;  mesoderm,  red;  entoderm 
and  notochord,  black. 


Umbilical 
cord 

Chorion 


Placenta 


Amnion 


Umbilical 
cord 


Yolk^ac 


Vitelline 
duct 


Fig.  30. — Fetua  of  about  eight  weeks,  enclosed  in  the  amnioa.     Magnified  a  little  over  two  diameters.     (Drawn 
from  stereoscopic  photographs  lent  by  Prof.  A.  Thomson,  Oxford.) 


length  of  the  fetus,  i.  e.,  about  50  cm.,  but  it  may  be  greatly  diminished  or  increased. 
The  rudiment  of  the  umbilical  cord  is  represented  by  the  tissue  which  connects- 
the  rapidly  growing  embryo  with  the  extra-embryonic  area  of  the  ovum.  Included 
in  this  tissue  are  the  body-stalk  and  the  vitelline  duct— the  former  containing  the 
allantoic  diverticulum  and  the  umbilical  vessels,  the  latter  forming  the  communica- 
tion between  the  digestive  tube  and  the  yolk-sac.  The  body-stalk  is  the  posterior 
segment  of  the  embryonic  area,  and  is  attached  to  the  chorion.  It  consists  of  a  plate 
of  mesoderm  covered  by  thickened  ectoderm  on  which  a  trace  of  the  neural  groove 
can  be  seen,  indicating  its  continuity  with  the  embryo.  Running  through  its 
mesoderm  are  the  two  umbilical  arteries  and  the  two  umbilical  veins,  together  with 
the  canal  of  the  allantois — the  last  being  lined  by  entoderm  (Fig.  31).  Its  dorsal] 
surface  is  covered  by  the  amnion,  while  its  ventral  surface  is  bounded  b}^  the  extra- 
embryonic celom,  and  is  in  contact  with  the  vitelline  duct  and  yolk-sac.  With 
the  rapid  elongation  of  the  embryo  and  the  formation  of  the  tail  fold,  the  body 
stalk  comes  to  lie  on  the  ventral  surface  of  the  embryo  (Figs.  27  and  28),  where 


Splanchnic 
mesoderm 
Entoderm, 


Vitelline  veins 


Somatic  iriesodemi 


Amniotic  cavity 
Amniofi 
Neural  groove 


Body-stalk 


Fig.  31. — Model  of  human  embryo  1.3  mm.  long,     (.\fter  Eternod.) 


its  mesoderm  blends  with  that  of  the  yolk-sac  and  the  vitelline  duct.  The  lateral 
leaves  of  somatopleure  then  grow  round  on  each  side,  and,  meeting  on  the  ventral 
aspect  of  the  allantois,  enclose  the  vitelline  duct  and  vessels,  together  with  a  part 
of  the  extra-embryonic  celom;  the  latter  is  ultimately  obliterated.  The  cord  is 
covered  by  a  layer  of  ectoderm  which  is  continuous  with  that  of  the  amnion,  and 
its  various  constitutents  are  enveloped  by  embryonic  gelatinous  tissue,  jelly  of 
Wharton.  The  vitelline  vessels  and  duct,  together  with  the  right  umbilical  vein, 
undergo  atrophy  and  disappear;  and  thus  the  cord,  at  birth,  contains  a  pair  of 
umbilical  arteries  and  one  (the  left)  umbilical  vein. 

Implantation  or  Imbedding  of  the  Ovum. — As  described  (page  44),  fertilization 
of  the  ovum  occurs  in  the  lateral  or  ampullary  end  of  the  uterine  tube  and  is 
immediately  followed  by  segmentation.  On  reaching  the  cavity  of  the  uterus  the 
segmented  ovum  adheres  like  a  parasite  to  the  uterine  mucous  membrane,  destroys 
the  epithelium  over  the  area  of  contact,  and  excavates  for  itself  a  cavity  in  the 
mucous  membrane  in  which  it  becomes  imbedded.     In  the  ovum  described  by 


DEVELOPMENT  OF  THE  FETAL  MEMBRANES  AND  THE  PLACENTA      59 


IBryce  and  Teacher^  the  point  of  entrance  was  visible  as  a  small  gap  closed  by  a 
mass  of  fibrin  and  leucocytes;  in  the  ovum  described  by  Peters^  the  opening  was 
covered  by  a  mushroom-shaped  mass  of  fibrin  and  blood-clot  (Fig.  32),  the  narrow 
stalk  of  which  plugged  the  aperture  in  the  mucous  membrane.  Soon,  however, 
^         all  trace  of  the  opening  is  lost  and  the  ovum  is  then  completely  surrounded  by  the 

It  uterine  mucous  membrane. 
The  structure  actively  concerned  in  the  process  of  excavation  is  the  trophoblast 
•  of  the  ovum,  which  possesses  the  power  of  dissolving  and  absorbing  the  uterine 
tissues.  The  trophoblast  proliferates  rapidly  and  forms  a  network  of  branching 
processes  which  cover  the  entire  ovum  and  invade  and  destroy  the  maternal 
^^  tissues  and  open  into  the  maternal  bloodvessels,  with  the  result  that  the  spaces 
^■(  in  the  trophoblastic  network  are  filled  w  ith  maternal  blood ;  these  spaces  com- 
1^^  municate  freely  with  one  another  and  become  greatly  distended  and  form  the 
intervillous  space. 

TTi.v.  tr.  a.Q.  tr. 


II 


F^o.  32. — Section  through  ovum  imbedded  in  the  uterine  decidua.  Semidiagrammatic.  (After  Peters.)  am. 
Ammotic  cavity,  h.c.  Blood-clot.  h.s.  Body-stalk,  ect.  Embryonic  ectoderm,  ent.  Entoderm,  mes.  Mesoderm. 
m.x.  Maternal  vessels,     tr.  Trophoblast.     u.e.  Uterine  epithelium,     u.g.  Uterine  glands,     j/.s.  Yolk-sac. 

The  Decidua. — Before  the  fertilized  ovum  reaches  the  uterus,  the  mucous 
membrane  of  the  body  of  the  uterus  undergoes  important  changes  and  is  then 
known  as  the  decidua.  The  thickness  and  vascularity  of  the  mucous  membrane 
are  greatly  increased;  its  glands  are  elongated  and  open  on  its  free  surface  by 
funnel-shaped  orifices,  while  their  deeper  portions  are  tortuous  and  dilated  into 
irregular  spaces.  The  interglandular  tissue  is  also  increased  in  quantity,  and 
is  crowded  with  large  round,  oval,  or  polygonal  cells,  termed  decidual  cells.  These 
changes  are  well  advanced  by  the  second  month  of  pregnancy,  when  the  mucous 
membrane  consists  of  the  following  strata  (Fig.  33):  (1)  stratum  compactum,  next 


>  Contribution  to  the  study  of  the  early  development  and  imbedding  of  the  human  ovum,  1908. 
'  Die  Einbettung  des  menschlichen  Eies,  1899. 


60 


EMBRYOLOGY 


MvxMus  membrane 


Muscular  fibers 


Stratum  compactum 


the  free  surface;  in  this  the  uterine  glands  are  only  slightly  expanded,  and  arej 
lined  by  columnar  cells;  (2)  stratum  spongiosum,  in  which  the  gland  tubes  are  greatly 
dilated  and  very  tortuous,  and  are  ultimately  separ-ated  from  one  another  by  only 
a  small  amount  of  interglandular  tissue,  while  their  lining  cells  are  flattened  or' 
cubical;  (3)  a  thin  unaltered  or  boundary  layer,  next  the  uterine  muscular  fibers, 
containing  the  deepest  parts  of  the  uterine  glands,  which  are  not  dilated,  and 

are  lined  with  columnar  epithelium; 
it  is  from  this  epithelium  that  the 
epithelial  lining  of  the  uterus  is  re- 
generated after  pregnancy.  Distinc- 
tive names  are  applied  to  different 
portions  of  the  decidua.  The  part 
which  covers  in  the  ovum  is  named  the 
decidua  capsularis;  the  portion  which 
intervenes  between  the  ovum  and  the 
uterine  wall  is  named  the  decidua 
basalis  or  decidua  placentalis ;  it  is  here 
that  the  placenta  is  subsequently 
developed.  The  part  of  the  decidua 
which  lines  the  remainder  of  the  body 
of  the  uterus  is  known  as  the  decidua 
vera  or  decidua  parietaUs. 

Coincidently  with  the  growth  of 
the  embryo,  the  decidua  capsularis  is 
thinned  and  extended  (Fig.  34)  and 
the  space  between  it  and  the  decidua 
vera  is  gradually  obliterated,  so  that 
by  the  third  month  of  pregnancy  the 
two  are  in  contact.  By  the  fifth 
month  of  pregnancy  the  decidua  cap- 
sularis has  practically  disappeared, 
while  during  the  succeeding  months 
the  decidua  vera  also  undergoes 
atrophy,  owing  to  the  increased  press- 
ure. The  glands  of  the  stratum  com- 
pactum are  obliterated,  and  their 
epithelium  is  lost.  In  the  stratum 
spongiosum  the  glands  are  compressed 
and  appear  as  slit-like  fissures,  while 
their  epithelium  undergoes  degener- 
ation. In  the  unaltered  or  boundary 
layer,  however,  the  glandular  epithe- 
lium retains  a  columnar  or  cubical 
form. 

The  Chorion  (Figs.  23  to  28)  .—The 
chorion  consists  of  two  layers :  an  outer 
formed  by  the  primitive  ectoderm  or 
trophoblast,  and  an  inner  by  the  soma- 
tic mesoderm;  with  this  latter  the  amnion  is  in  contact.  The  trophoblast  is  made 
up  of  an  internal  layer  of  cubical  or  prismatic  cells,  the  c3rtotrophoblast  or  layer 
of  Langhans,  and  an  external  layer  of  richly  nucleated  protoplasm  devoid  of  cell 
boundaries,  the  syncytiotrophoblast.  It  undergoes  rapid  proliferation  and  forms 
numerous  processes,  the  chorionic  villi,  which  invade  and  destroy  the  uterine 
decidua  and  at  the  same  time  absorb  from  it  nutritive  materials  for  the  growth 


Stratum  spongiosum 


Unaltered  or 
boundary  layer 

Muscular  fibers 


Fig.  33. — Diagrammatic  sections  of  the  uterine  mucous 
membrane:  A.  The  non-pregnant  uterus.  B.  The  preg- 
nant uterus,  showing  the  thickened  mucous  membrane 
and  the  altered  condition  of  the  uterine  glands.  (Kundrat 
and  Engelmann.) 


I 


DEVELOPMENT  OP   THE  FETAL  MEMBRANES  AND  THE  PLACENTA     61 


of  the  embryo.  The  chorionic  villi  are  at  first  small  and  non-vascular,  and  consist 
of  trophoblast  only,  but  they  increase  in  size  and  ramify,  while  the  mesoderm, 
carrying  branches  of  the  umbilical  vessels,  grows  into  them,  and  in  this  way  they 
are  vascularized.     Blood  is  carried  to  the  villi  by  the  branches  of  the  umbilical 

Placeyital  villi  imbedded  in  the 

^Decidua  placentalis 

Uterine  tvhe 


Allantois 


Umbilical  cord 
with  its  con- 
tained vessels 


Non-placental  villi  im- 
bedded in  the  decidua 
capsularis 


Cavity  of  uterus 
Yolk-sac 

Cavity  of  amnion 

Decidua  vera 
or  parietalis 


Plug  of  rnucus  in  the 
cervix  uteri 


Fig.  34. — Sectional  plan  of  the  gravid  uterus  in  the  third  and  fourth  month.     (Modified  from  Wagner.) 

arteries,  and  after  circulating  through  the  capillaries  of  the  villi,  is  returned  to 
the  embryo  by  the  umbilical  veins.  Until  about  the  end  of  the  second  month 
of  pregnancy  the  villi  cover  the  entire  chorion,  and  are  almost  uniform  in  size 
(Fig.  25),  but  after  this  they  develop  unequally.    The  greater  part  of  the  chorion 


Trophoblast 


esoderm 


Branches  of  umbilical  i 
Fig.  35. — Transverse  section  of  a  chorionic  villus 


is  in  contact  with  the  decidua  capsularis  (Fig.  34),  and  over  this  portion  the  villi, 

with  their  contained  vessels,  undergo  atrophy,  so  that  by  the  fourth  month  scarcely 

.  a  trace  of  them  is  left,  and  hence  this  part  of  the  chorion  becomes  smooth,  and  is 

named  the  chorion  Iseve;  as  it  takes  no  share  in  the  formation  of  the  placenta,  it 


62 


EMBRYOLOGY 


is  also  named  the  non-placental  part  of  the  chorion.  On  the  other  hand,  the  villi 
on  that  part  of  the  chorion  which  is  in  contact  with  the  decidua  placentalis  increase 
greatly  in  size  and  complexity,  and  hence  this  part  is  named  the  chorion  frondosum 
(Fig.  28). 


Uterine  vessels 


Uterine  glands 


Syncytiolroj)h6blast 
Cytolrophoblast 


Mesoderm  Intervilloiis  space 

Fig.  36. — Primary  chorionic  villi.     Diagrammatic.     (Modified  from  Bryce. 

The  Placenta. — The  placenta  connects  the  fetus  to  the  uterine  wall,  and  is  the 
organ  by  means  of  which  the  nutritive,  respiratory,  and  excretory  functions  of  the 
fetus  are  carried  on.    It  is  composed  of  fetal  and  maternal  portions. 

Fetal  Portion. — The  fetal  portion  of  the  placenta  consists  of  the  villi  of  the 
chorion  frondosum;  these  branch  repeatedly,  and  increase  enormously  in  size. 
These  greatly  ramified  villi  are  suspended  in  the  intervillous  space,  and  are  bathed 


Uterine  glands 


Uterine  vessels 


Syncytiotrophoblast 

Cytolrophoblast 

Core  of  mesoderm 

with  fetal  vessels 


Mesoderm  Intervillous  space 

Fig.  37. — Secondary  chorionic  villi.     Diagrammatic.      (Modified  from  Bryce.) 

in  maternal  blood,  which  is  conveyed  to  the  space  by  the  uterine  arteries  and 
carried  away  by  the  uterine  veins.  A  branch  of  an  umbilical  artery  enters  each 
villus  and  ends  in  a  capillary  plexus  from  which  the  blood  is  drained  by  a  tributary 
of  the  umbilical  vein.  The  vessels  of  the  villus  are  surrounded  by  a  thin  layer  of 
mesoderm  consisting  of  gelatinous  connective  tissue,  which  is  covered  by  two 


DEVELOPMENT  OF  THE  FETAL  MEMBRANES  AND  THE  PLACENTA     63 

strata  of  ectodermal  cells  derived  from  the  trophoblast :  the  deeper  stratum, 
next  the  mesodermic  tissue,  represents  the  cytotrophoblast  or  layer  of  Langhans; 
the  fiuperficial,  in  contact  with  the  maternal  blood,  the  syncytiotrophoblast  (Figs. 
3(3  and  37).  After  the  fifth  month  the  two  strata  of  cells  are  replaced  by  a 
single  layer  of  somewhat  flattened  cells. 

Maternal  Portion. — The  maternal  portion  of  the  placenta  is  formed  by  the 
decidua  placentalis  containing  the  intervillous  space.  As  already  explained,  this 
space  is  produced  by  the  enlargement  and  intercommunication  of  the  spaces  in 
the  trophoblastic  network.  The  changes  involve  the  disappearance  of  the  greater 
portion  of  the  stratum  compactum,  but  the  deeper  part  of  this  layer  persists  and 
is  condensed  to  form  what  is  known  as  the  basal  plate.  Between  this  plate  and 
the  uterine  muscular  fibres  are  the  stratum  spongiosum  and  the  boundary  layer ; 


Wall  of  uterus 


Umbilical  cord 


Cervix  uteri 


Fio.  38. — Fetus  in  utero,  between  fifth  and  sixth  months. 


through  these  and  the  basal  plate  the  uterine  arteries  and  veins  pass  to  and  from 
the  intervillous  space.  The  endothelial  lining  of  the  uterine  vessels  ceases  at  the 
point  where  they  terminate  in  the  intervillous  space  w^hich  is  lined  by  the  syncytio- 
trophoblast. Portions  of  the  stratum  compactum  persist  and  are  condensed  to 
form  a  series  of  septa,  which  extend  from  the  basal  plate  through  the  thickness 
of  the  placenta  and  subdivide  it  into  the  lobules  or  cotyledons  seen  on  the  uterine 
surface  of  the  detached  placenta. 

The  fetal  and  maternal  blood  currents  traverse  the  placenta,  the  former  passing 
through  the  bloodvessels  of  the  placental  villi  and  the  latter  through  the  inter- 

I villous  space  (Fig.  39).  The  two  currents  do  not  intermingle,  being  separated  from 
each  other  by  the  delicate  walls  of  the  villi.    Nevertheless,  the  fetal  blood  is  able 


64 


EMBRYOLOGY 


I 


maternal  blood,  and  give  up  to  the  latter  its  waste  products.  The  blood,  so  purified , 
is  carried  back  to  the  fetus  by  the  umbilical  vein.  It  will  thus  be  seen  that  the 
placenta  not  only  establishes  a  mechanical  connection  between  the  mother  and  the 
fetus,  but  subserves  for  the  latter  the  purposes  of  nutrition,  respiration,  and  ex- 
cretion. In  favor  of  the  view  that  the  placenta  possesses  certain  selective  powers 
may  be  mentioned  the  fact  that  glucose  is  more  plentiful  in  the  maternal  than  in 
the  fetal  blood.  It  is  interesting  to  note  also  that  the  proportion  of  iron,  and  of 
lime  and  potash,  in  the  fetus  is  increased  during  the  last  months  of  pregnancy. 
Further,  there  is  evidence  that  the  maternal  leucocytes  may  migrate  into  the  fetal 
blood,  since  leucocytes  are  much  more  numerous  in  the  blood  of  the  umbilical  vein 
than  in  that  of  the  umbilical  arteries. 

The  placenta  is  usually  attached  near  the  fundus  uteri,  and  more  frequently  on 
the  posterior  than  on  the  anterior  wall  of  the  uterus.  It  may,  however,  occupy 
a  lower  position  and,  in  rare  cases,  its  site  is  close  to  the  orificium  internum  uteri, 
which  it  may  occlude,  thus  giving  rise  to  the  condition  known  as  placenta  previa. 


Stratum  spongiosum 
Limiting  or  boundary  layer 
Maternal  vessels 


Placental  septum 


ViUiLs 


Chorion 
Marginal  sinus 


Fig.  39. — Scheme  of  placental  circulation. 

Separation  of  the  Placenta. — ^After  the  child  is  born,  the  placenta  and  membranes 
are  expelled  from  the  uterus  as  the  after-birth.  The  separation  of  the  placenta  from 
the  uterine  wall  takes  place  through  the  stratum  spongiosum,  and  necessarily 
causes  rupture  of  the  uterine  vessels.  The  orifices  of  the  torn  vessels  are,  however, 
closed  by  the  firm  contraction  of  the  uterine  muscular  fibers,  and  thus  postpartum 
hemorrhage  is  controlled.  The  epithelial  lining  of  the  uterus  is  regenerated  by  the 
proliferation  and  extension  of  the  epithelium  which  lines  the  persistent  portions 
of  the  uterine  glands  in  the  unaltered  layer  of  the  decidua. 

The  expelled  placenta  appears  as  a  discoid  mass  which  weighs  about  450  gm. 
and  has  a  diameter  of  from  15  to  20  cm.  Its  average  thickness  is  about  3  cm., 
but  this  diminishes  rapidly  toward  the  circumference  of  the  disk,  which  is  continu- 
ous with  the  membranes.  Its  uterine  surface  is  divided  by  a  series  of  fissures  into 
lobules  or  cotyledons,  the  fissures  containing  the  remains  of  the  septa  which  extended 
between  the  maternal  and  fetal  portions.  Most  of  these  septa  end  in  irregular 
or  pointed  processes;  others,  especially  those  near  the  edge  of  the  placenta,  pass 


THE  BRANCHIAL  REGION 


65 


through  its  thickness  and  are  attached  to  the  chorion.  In  the  early  months  these 
septa  convey  branches  of  the  uterine  arteries  which  open  into  the  intervillous 
space  on  the  surfaces  of  the  septa.  The  fetal  surface  of  the  placenta  is  smooth, 
being  closely  invested  by  the  amnion.  Seen  through  the  latter,  the  chorion 
presents  a  mottled  appearance,  consisting  of  gray,  purple,  or  yellowish  areas. 
The  umbilical  cord  is  usually  attached  near  the  center  of  the  placenta,  but 
may  be  inserted  anywhere  between  the  center  and  the  margin;  in  some  cases  it 
is  inserted  into  the  membranes,  i.  e.,  the  velamentous  insertion.  From  the  attach- 
ment of  the  cord  the  larger  branches  of  the  umbilical  vessels  radiate  under  the 
amnion,  the  veins  being  deeper  and  larger  than  the  arteries.  The  remains  of 
the  vitelline  duct  and  yolk-sac  may  be  sometimes  observed  beneath  the  amnion, 
close  to  the  cord,  the  former  as  an  attenuated  thread,  the  latter  as  a  minute  sac. 
,  On  section,  the  placenta  presents  a  soft,  spongy  appearance,  caused  by  the 
Ugreatly  branched  villi;  surrounding  them  is  a  varying  amount  of  maternal  blood 
giving  the  dark  red  color  to  the  placenta.  Many  of  the  larger  villi  extend  from 
the  chorionic  to  the  decidual  surface,  while  others  are  attached  to  the  septa  which 
separate  the  cotyledons;  but  the  great  majority  of  the  villi  hang  free  in  the  inter- 
villous space. 


Mid-brain 


Fore-brain 
Stomodeum 
andibtdar  arch 
Heart 


Hind-brain 

Auditory  vesicle 


Visceral 
arches 


Olfactory  pit 
Maxillary  process 
Amnion  (cut)  Mandibular  arch 

Hyoid  arch 

Third  arch 


Body-stalk 

Fio.  40. — Embryo  between  eighteen  and  twenty-one 
days.     (His.) 


Fig.  4t. — Head  end  of  human  embryo,  about  the  end 
of  the  fourth  week.    (From  model  by  Peter.) 


THE  BRANCHIAL  REGION. 

The  Branchial  or  Visceral  Arches  and  Pharyngeal  Pouches. — In  the  lateral  walls 
of  the  anterior  part  of  the  fore-gut  five  pharyngeal  pouches  appear  (Fig.  42) ;  each 
of  the  upper  four  pouches  is  prolonged  into  a  dorsal  and  a  ventral  diverticulum. 
Over  these  pouches  corresponding  indentations  of  the  ectoderm  occur,  forming  what 
are  known  as  the  branchial  or  outer  pharjnageal  grooves.  The  intervening  mesoderm 
is  pressed  aside  and  the  ectoderm  comes  for  a  time  into  contact  with  the  ento- 
dermal  lining  of  the  fore-gut,  and  the  two  layers  unite  along  the  floors  of  the 
grooves  to  form  thin  closing  membranes  between  the  fore-gut  and  the  exterior. 
Later  the  mesoderm  again  penetrates  between  the  entoderm  and  the  ectoderm. 
In  gill-bearing  animals  the  closing  membranes  disappear,  and  the  grooves  become 
5 


66 


EMBRYOLOGY 


I 


Lateral  tongue    Thyroid, 
elevations     diverticvium 


complete  clefts,  the  gill-clefts,  opening  from  the  pharynx  on  to  the  exterior;  p^ 
ration,  however,  does  not  occur  in  birds  or  mammals.  The  grooves  separate  a 
series  of  rounded  bars  or  arches,  the  branchial  or  visceral  arches,  in  which  thickening 
of  the  mesoderm  takes  place  (Figs.  40  and  41).  The  dorsal  ends  of  these  arches 
are  attached  to  the  sides  of  the  head,  while  the  ventral  extremities  ultimately 
meet  in  the  middle  line  of  the  neck.  In  all,  six  arches  make  their  appearance, 
but  of  these  only  the  first  four  are  visible  externally.    The  first  arch  is  named  the 

mandibular,  and  the  second  the  hyoid;  the 
others  have  no  distinctive  names.  In  each 
arch  a  cartilaginous  bar,  consisting  of  right 
and  left  halves,  is  developed,  and  with  each 
of  these  there  is  one  of  the  primitive  aortic 
arches.  Ml 

The  mandibular  arch  lies  between  the  first^^ 
branchial  groove  and  the  stomodeum;  from  it 
are  developed  the  lower  lip,  the  mandible, 
the  muscles  of  mastication,  and  the  anterior 
part  of  the  tongue.  Its  cartilaginous  bar  is 
formed  by  what  are  known  as  Meckel's  carti- 
lages (right  and  left)  (Fig.  43) ;  above  this  the 
incus  is  developed.  The  dorsal  end  of  each 
cartilage  is  connected  with  the  ear-capsule 
and  is  ossified  to  form  the  malleus;  the  ventral  ends  meet  each  other  in  the  region 
of  the  symphysis  menti,  and  are  usually  regarded  as  undergoing  ossification  to  form 
that  portion  of  the  mandible  which  contains  the  incisor  teeth.  The  intervening 
part  of  the  cartilage  disappears;  the  portion  immediately  adjacent  to  the  malleus  is 
replaced  by  fibrous  membrane,  which  constitutes  the  spheno-mandibular  ligament, 


Malleus 


Entrance  to 
larynx 


Fia.  42. — Floor  of  pharynx  of  embryo  shown  in 
Fig.  40. 


Incus 


Tympanic  ring 
'  Mandible 


• —  Meckel's  cartilage 


Hyoid  bone 


Fia.  43. — Head  and  neck  of  a  human  embryo  eighteen  weeks  old,  with  Meckel's  cartilage  and  hyoid  bar  exposed 

(After  Kolliker.) 


while  from  the  connective  tissue  covering  the  remainder  of  the  cartilage  the  greater 
part  of  the  mandible  is  ossified.  From  the  dorsal  ends  of  the  mandibular  arch  a 
triangular  process,  the  maxillary  process,  grows  forward  on  either  side  and  forms 
the  cheek  and  lateral  part  of  the  upper  lip.  The  second  or  hyoid  arch  assists  in 
forming  the  side  and  front  of  the  neck.  From  its  cartilage  are  developed  the  styloid 
process,  stylohyoid  ligament,  and  lesser  cornu  of  the  hyoid  bone.    The  stages  prob- 


1 


THE  BRANCHIAL  REGION 


67 


ably  arises  in  the  upper  part  of  this  arch.  The  cartilage  of  the  third  arch  gives  origin 
to  the  greater  cornu  of  the  hyoid  bone.  The  ventral  ends  of  the  second  and  third 
arches  unite  with  those  of  the  opposite  side,  and  form  a  transverse  band,  from 
which  the  body  of  the  hyoid  bone  and  the  posterior  part  of  the  tongue  are  devel- 
oped. The  ventral  portions  of  the  cartilages  of  the  fourth  and  fifth  arches  unite 
to  form  the  thyroid  cartilage;  from  the  cartilages  of  the  sixth  arch  the  cricoid 
and  arytenoid  cartilages  and  the  cartilages  of  the  trachea  are  developed.  The 
mandibular  and  hyoid  arches  grow  more  rapidly  than  those  behind  them,  with 
the  result  that  the  latter  become,  to  a  certain  extent,  telescoped  within  the 
former,  and  a  deep  depression,  the  sinus  cervicalis,  is  formed  on  either  side  of 
the  neck.  This  sinus  is  bounded  in  front  by  the  hyoid  arch,  and  behind  by  the 
thoracic  wall;  it  is  ultimately  obliterated  by  the  fusion  of  its  walls. 

From  the  first  branchial  groove  the  concha  auriculae  and  external  acoustic 
meatus  are  developed,  while  around  the  groove  there  appear,  on  the  mandibular 
and  hyoid  arches,  a  number  of  swellings  from  which  the  auricula  or  pinna  is  formed. 
The  first  pharyngeal  pouch  is  prolonged  dorsally  to  form  the  auditory  tube  and  the 
tympanic  cavity;  the  closing  membrane  between  the  mandibular  and  hyoid  arches 

Membranous  capsule  over  cerebral  7iemisj)here 


Fronto-nasal  process 


Stomodeum 


Lateral  nasal  process 

Eye 

Globular  process 
Maxillary  process 

Mandibular  arch 
Hyomandibvlar  deft 


Fig.  44. — Under  surface  of  the  head  of  a  human  embryo  about  twenty-nine  days  old.     (After  His.) 

is  invaded  by  mesoderm,  and  forms  the  tympanic  membrane.  No  traces  of  the 
second,  third,  and  fourth  branchial  grooves  persist.  The  inner  part  of  the  second 
pharyngeal  pouch  is  named  the  sinus  tonsillaris;  in  it  the  tonsil  is  developed,  above 
which  a  trace  of  the' sinus  persists  as  the  supratonsillar  fossa.  The  fossa  of  Rosen- 
miiller  or  lateral  recess  of  the  pharynx  is  by  some  regarded  as  a  persistent  part  of 
the  second  pharyngeal  pouch,  but  it  is  probably  developed  as  a  secondary  forma- 
tion. From  the  third  pharyngeal  pouch  the  thymus  arises  as  an  entodermal  diver- 
ticulum on  either  side,  and  from  the  fourth  pouches  small  diverticula  project  and 
become  incorporated  with  the  thymus,  but  in  man  these  diverticula  probably 
never  form  true  thymus  tissue.  The  parathyroids  also  arise  as  diverticula  from 
the  third  and  fourth  pouches.  From  the  fifth  pouches  the  ultimobranchial  bodies 
originate  and  are  enveloped  by  the  lateral  prolongations  of  the  median  thyroid 
rudiment;  they  do  not,  however,  form  true  thyroid  tissue,  nor  are  any  traces 
of  them  found  in  the  human  adult. 

The  Nose  and  Face. — During  the  third  week  two  areas  of  thickened  ectoderm,  the 
olfactory  areas,  appear  immediately  under  the  fore-brain  in  the  anterior  wall  of  the 
stomodeum,  one  on  either  side  of  a  region  termed  the  fronto-nasal  process  (Fig.  44). 
By  the  upgrowth  of  the  surrounding  parts  these  areas  are  converted  into  pits, 


68 


EMBRYOLOGY 


the  olfactory  pits,  which  indent  the  fronto-nasal  process  and  divide  it  into  a 
medial  and  two  lateral  nasal  processes  (Fig.  45).  The  rounded  lateral  angles  ol 
the  medial  process  constitute  the  globular  processes  of  Plis.  The  olfactory  pits  form 


I 


Future  apex  of  nose 

Medial  nasal  frocesa 

Oljactory  -pit 
Lateral  rmsal  process 
Olcbular  ^ocess 
Maxillary  process 
Stomodeura 
Mandibular  arch 


Future  apex  of  nose 

Medial  nasal  process 

Olfactory  pit 

Lateral  nasal  process 

Globular  process 
Maxillary  process 

Rocf  of  pharynx 
Hypophyseal  diverticulum 
Dorsal  wall  of  pharynx 


Fig.  45. — Head  end  of  human  embryo  of  about  thirty 
to  thirty-one  days.    (From  model  by  Peters.) 


Fig.  46. — Same  embryo  as  shown  in  Fig.  45,  with  front 
wall  of  pharynx  removed. 


the  rudiments  of  the  nasal  cavities,  and  from  their  ectodermal  lining  the  epithe- 
lium of  the  nasal  cavities,  with  the  exception  of  that  of  the  inferior  meatuses,  is 
derived.  The  globular  processes  are  prolonged  backward  as  plates,  termed  the  nasal 
laminae :  these  laminse  are  at  first  some  distance  apart,  but,  gradually  approach- 


Lateral  nasal  pro- 
cess 
Olobvlar  processes 


Fig.  47. — Head  of  a  human  embryo  of 
about  eight  weeks,  in  which  the  nose  and 
mouth  are  formed.     (His.) 


Fig.  48. — Diagram  showing  the  regions  of  the  adult  face  and  neck 
related  to  the  fronto-nasal  process  and  the  branchial  arches. 


ing,  they  ultimately  fuse  and  form  the  nasal  septum;  the  processes  themselves 
meet  in  the  middle  line,  and  form  the  premaxillse  and  the  philtrum  or  central 
part  of  the  upper  lip  (Fig.  48).    The  depressed  part  of  the  medial  nasal  process 


THE  BRANCHIAL  REGION 


69 


)etv\'een  the  globular  processes  forms  the  lower  part  of  the  nasal  septum  or 
columella;  while  above  this  is  seen  a  prominent  angle,  which  becomes  the  future 
apex  (Figs.  45,  46),  and  still  higher  a  flat  area,  the  future  bridge,  of  the  nose. 
The  lateral  nasal  processes  form  the  alse  of  the  nose. 

'  Continuous  with  the  dorsal  end  of  the  mandibular  arch,  and  growing  forward 
from  its  cephalic  border,  is  a  triangular  process,  the  maxillary  process,  the  ventral 
extremity  of  which  is  separated  from  the  mandibular  arch  by  a  >  shaped  notch 


Narea 


Primitive 
palate 


Nasal 
cavity 


Bucconasal 
membranes 

Fig.  49. — Primitive  palate  of  a  human  embryo  of  thirty-seven  to  thirty-eight  days.     (From  model  by  Peters.) 
On  the  left  side  the  lateral  waU  of  the  nasal  cavity  has  been  removed. 

(Fig.  44).  The  maxillary  process  forms  the  lateral  wall  and  floor  of  the  orbit, 
and  in  it  are  ossified  the  zygomatic  bone  and  the  greater  part  of  the  maxilla;  it 
meets  with  the  lateral  nasal  process,  from  which,  however,  it  is  separated  for  a 
time  by  a  groove,  the  naso-optic  furrow,  that  extends  from  the  furrow  encircling 
the  eyeball  to  the  olfactory  pit.  The  maxillary  processes  ultimately  fuse  with  the 
ateral  nasal  and  globular  processes,  and  form  the  lateral  parts  of  the  upper  lip 


Gldbvlar  'process 


Mouth  of  olfactory 
pit,  or  naris 


Palatine  process  of 
globular  process 

Palatine  part  of 
maxillary  process 


Maxillary  process 


Pharynx 


Fig.  50. — The  roof  of  the  mouth  of  a  human  embryo,  aged  about  two  and  a  half  months,  showing  the  mode  of 

formation  of  the  palate.     (His.) 


I 


and  the  posterior  boundaries  of  the  nares  (Figs.  47,  48).  From  the  third  to 
the  fifth  month  the  nares  are  filled  by  masses  of  epithelium,  on  the  breaking  down 
and  disappearance  of  which  the  permanent  openings  are  produced.  The  maxillary 
process  also  gives  rise  to  the  lower  portion  of  the  lateral  wall  of  the  nasal  cavity. 
The  roof  of  the  nose  and  the  remaining  parts  of  the  lateral  wall,  viz.,  the  ethmoidal 
labyrinth,  the  inferior  nasal  concha,  the  lateral  cartilage,  and  the  lateral  crus  of 
the  alar  cartilage,  are  developed  in  the  lateral  nasal  process.    By  the  fusion  of  the 


70 


EMBRYOLOGY 


I 


maxillary  and  nasal  processes  in  the  roof  of  the  stomodeum  the  primitive  palate 
(Fig.  49)  is  formed,  and  the  olfactory  pits  extend  backward  above  it.  The  pos- 
terior end  of  each  pit  is  closed  by  an  epithelial  membrane,  the  bucco-nasal  membrane, 
formed  by  the  apposition  of  the  nasal  and  stomodeal  epithelium.  By  the  rupture^! 
of  these  membranes  the  primitive  choanse  or  openings  between  the  olfactory  pits 
and  the  stomodeum  are  established.  The  floor  of  the  nasal  cavity  is  completed 
by  the  development  of  a  pair  of  shelf-like  palatine  processes  which  extend  medial- 
ward  from  the  maxillary  processes  (Figs.  50  and  51);  these  coalesce  with  each 
other  in  the  middle  line,  and  constitute  the  entire  palate,  except  a  small  part  in 
front  which  is  formed  by  the  premaxillary  bones.  Two  apertures  persist  for  a  time 
between  the  palatine  processes  and  the  premaxillse  and  represent  the  permanent 
channels  which  in  the  lower  animals  connect  the  nose  and  mouth.  The  union  of 
the  parts  which  form  the  palate  commences  in  front,  the  premaxillary  and  palatine 
processes  joining  in  the  eighth  week,  while  the  region  of  the  future  hard  palate 


Lateral  part  of_ 
nasal  capsule 


Inferior  concha 


Inferior  meatus 

Vomeronasal         ^^-a^-'S^-v 
cartilage  '    ' 


Palatine  process 


Cartilage  of 
'^!^  nasal  septum 


Vomeronasal 
organ  of  Jacobson 


Inferior  meatus 


Cavity  of  mouth 


Fig.  51. — Frontal  section  of  nasal  cavities  of  a  human  embryo  28  mm.  long.     (Kollmann.) 

is  completed  by  the  ninth,  and  that  of  the  soft  palate  by  the  eleventh  week.  By 
the  completion  of  the  palate  the  permanent  choanse  are  formed  and  are  situated  a 
considerable  distance  behind  the  primitive  choanse.  The  deformity  known  as 
cleft  palate  results  from  a  non-union  of  the  palatine  processes,  and  that  of  hare- 
lip through  a  non-union  of  the  maxillary  and  globular  processes  (see  page  199). 
The  nasal  cavity  becomes  divided  by  a  vertical  septum,  which  extends  downward 
and  backward  from  the  medial  nasal  process  and  nasal  laminae,  and  unites  below 
with  the  palatine  processes.  Into  this  septum  a  plate  of  cartilage  extends  from 
the  under  aspect  of  the  ethmoid  plate  of  the  chodrocranium.  The  anterior  part 
of  this  cartilaginous  plate  persists  as  the  septal  cartilage  of  the  nose  and  the  medial 
crus  of  the  alar  cartilage,  but  the  posterior  and  upper  parts  are  replaced  by  the 
vomer  and  perpendicular  plate  of  the  ethmoid.  On  either  side  of  the  nasal  septum, 
at  its  lower  and  anterior  part,  the  ectoderm  is  invaginated  to  form  a  blind  pouch 
or  diverticulum,  which  extends  backward  and  upward  into  the  nasal  septum  and 
is  supported  by  a  curved  plate  of  cartilage.    These  pouches  form  the  rudiments  of 


THE  BRANCHIAL  REGION 


71 


le  vomero-nasal  organs  of  Jacobson,  which   open  below,  close  to  the  junction 
[of  the  premaxillary  and  maxillary  bones. 

The  Limbs. — The  limbs  begin  to  make  their  appearance  in  the  third  week  as 
[small  elevations  or  buds  at  the  side  of  the  trunk  (Fig.  52).  Prolongations  from 
[the  muscle-  and  cutis-plates  of  several  primitive  segments  extend  into  each  bud, 
and  carry  with  them  the  anterior  divisions  of  the  corresponding  spinal  nerves. 
The  nerves  supplying  the  limbs  indicate  the  number  of  primitive  segments  which 
contribute  to  their  formation — the  upper  limb  being  derived  from  seven,  viz., 
fourth  cervical  to  second  thoracic  inclusive,  and  the  lower  limb  from  ten,  viz., 
twelfth  thoracic  to  fourth  sacral  inclusive.  The  axial  part  of  the  mesoderm  of 
the  limb-bud  becomes  condensed  and  converted  into  its  cartilaginous  skeleton, 
and  by  the  ossification  of  this  the  bones  of  the  limbs  are  formed.  By  the  sixth 
week  the  three  chief  divisions  of  the  limbs  are  marked  off  by  furrows — the  upper 
into  arm,  forearm,  and  hand;  the  lower  into  thigh,  leg,  and  foot  (Fig.  53).  The 
limbs  are  at  first  directed  backward  nearly  parallel  to  the  long  axis  of  the  trunk. 


Heart 


Hyoid  arch 
Mandibvlar  arch 

Maxillary  process 


Auricula 


-  Fore-limb 


—Hind-limb 


Hg.  52. — Human  embryo  from  thirty-one  to  thirty- 
four  days.     (His.) 


Umbilical  cord 

Fig.  53. — Embryo  of  about  six  weeks.     (His. 


and  each  presents  two  surfaces  and  two  borders.  Of  the  surfaces,  one— the  future 
flexor  surface  of  the  limb — is  directed  ventrally;  the  other,  the  extensor  surface, 
dorsally;  one  border,  the  preaxial,  looks  forward  toward  the  cephalic  end  of  the 
embryo,  and  the  other,  the  postaxial,  backward  toward  the  caudal  end.  The  lateral 
epicondyle  of  the  humerus,  the  radius,  and  the  thumb  lie  along  the  preaxial  border 
of  the  upper  limb ;  and  the  medial  epicondyle  of  the  femur,  the  tibia,  and  the  great 
toe  along  the  corresponding  border  of  the  lower  limb.  The  preaxial  part  is  derived 
from  the  anterior  segments,  the  postaxial  from  the  posterior  segments  of  the  limb- 
bud;  and  this  explains,  to  a  large  extent,  the  innervation  of  the  adult  limb,  the 
nerves  of  the  more  anterior  segments  being  distributed  along  the  preaxial  (radial 
or  tibial),  and  those  of  the  more  posterior  along  the  postaxial  (ulnar  or  fibular) 
border  of  the  limb.  The  limbs  next  undergo  a  rotation  or  torsion  through  an  angle 
of  90°  around  their  long  axes  the  rotation  being  effected  almost  entirely  at  the 
limb  girdles.  In  the  upper  limb  the  rotation  is  outward  and  forward;  in  the  lower 
b,  inward  and  backward.    As  a  consequence  of  this  rotation  the  preaxial  (radial) 


Htlim 


72 


EMBRYOLOGY 


border  of  the  fore-limb  is  directed  lateralward,  and  the  preaxial  (tibial)  borde 
of  the  hind-limb  is  directed  medialward;  thus  the  flexor  surface  of  the  fore-limb 
is  turned  forward,  and  that  of  the  hind-limb  backward. 


DEVELOPMENT  OF  THE  BODY  CAVITIES. 


«l 


In  the  human  embryo  described  by  Peters  the  mesoderm  outside  the  embryonic 
disk  is  split  into  two  layers  enclosing  an  extra-embryonic  coelom;  there  is  no  trace 
of  an  intra-embryonic  coelom.  At  a  later  stage  four  cavities  are  formed  within  the 
embryo,  viz.,  one  on  either  side  within  the  mesoderm  of  the  pericardial  area,  and 
one  in  either  lateral  mass  of  the  general  mesoderm.  All  these  are  at  first  independent 
of  each  other  and  of  the  extra-embryonic  celom,  but  later  they  become  continuous. 
The  two  cavities  in  the  general  mesoderm  unite  on  the  ventral  aspect  of  the  gut 
and  form  the  pleuro-peritoneal  cavity,  which  becomes  continuous  with  the  remains 
of  the  extra-embryonic  celom  around  the  umbilicus;  the  two  cavities  in  the  peri- 
cardial area  rapidly  join  to  form  a  single  pericardial  cavity,  and  this  from  two  lateral 
diverticula  extend  caudalward  to  open  into  the  pleuro-peritoneal  cavity  (Fig.  54). 


y'^^K 


Mesentery 


Pleural  cavity  \^ 


lAi/ng. 


Pleuro-  pericardial 
opening 


Pericardium 


Mesoderm 

surrounding 

duct  ofCuvier 


"-^Dorsal  mesocardium 
~^Heart 


Fig.  64. — Figure  obtained  by  combining  several  successive  sections  of  a  human  embryo  of  about  the  fourth  week 
(From  KoUmann.)     The  upper  arrow  is  in  the  pleuroperitoneal  opening,  the  lower  in  the  pleuropericardial. 


Between  the  two  latter  diverticula  is  a  mass  of  mesoderm  containing  the  ducts 
of  Cuvier,  and  this  is  continuous  ventrally  with  the  mesoderm  in  which  the  umbili- 
cal veins  are  passing  to  the  sinus  venosus.  A  septum  of  mesoderm  thus  extends 
across  the  body  of  the  embryo.  It  is  attached  in  front  to  the  body-wall  between 
the  pericardium  and  umbilicus;  behind  to  the  body-wall  at  the  level  of  the  second 
cervical  segment;  laterally  it  is  deficient  where  the  pericardial  and  pleuro-peri- 
toneal cavities  communicate,  while  it  is  perforated  in  the  middle  line  by  the  fore- 
gut.  This  partition  is  termed  the  septum  transversum,  and  is  at  first  a  bulky  plate 
of  tissue.  As  development  proceeds  the  dorsal  end  of  the  septum  is  carried  grad- 
ually caudalward,  and  when  it  reaches  the  fifth  cervical  segment  muscular  tissue 
with  the  phrenic  nerve  grows  into  it.  It  continues  to  recede,  however,  until  it 
reaches  the  position  of  the  adult  diaphragm  on  the  bodies  of  the  upper  lumbar 
vertebrae.  The  liver  buds  grow  into  the  septum  transversum  and  undergo 
development  there. 

The  lung  buds  meantime  have  grown  out  from  the  fore-gut,  and  project  laterally 
into  the  forepart  of  the  pleuro-peritoneal  cavity;  the  developing  stomach  and  liver 
are  imbedded  in  the  septum  transversum;  caudal  to  this  the  intestines  project  into 
the  back  part  of  the  pleuro-peritoneal  cavity  (Fig.  55) .    Owing  to  the  descent  of 


I 


DEVELOPMENT  OF  THE  BODY  CAVITIES 


73 


the  dorsal  end  of  the  septum  transversum  the  lung  buds  come  to  lie  above  the 
septum  and  thus  pleural  and  peritoneal  portions  of  the  pleuro-peritoneal  cavity 
(still,  however,  in  free  communication  with  one  another)  may  be  recognized;  the 
pericardial  cavity  opens  into  the  pleural  part. 


Left  due  of  Cuvier       Hsopluxgus     Right  duct  of  Cuvier 


Omental  bursa 


Stomach 


2Iesoderm 

surrounding  duct 

Pleuro-pericardial 

opening 
Ridge  growing  across 

opening 

Dorsal  mesentery 
Peritoneal  recess 


Fia.  55. — Upper  part  of  celom  of  human  embryo  of  6.8  mm.,  seen  from  behind.     (From  model  by  Piper.) 

The  ultimate  separation  of  the  permanent  cavities  from  one  another  is  effected 
by  the  growth  of  a  ridge  of  tissue  on  either  side  from  the  mesoderm  surrounding 


Bsophagua 


Aorta 

Pleural  cavity 
Lung 

Inferior  vena  cava 


Body  wall 
Pericardium 


Fig.  56. — Diagram  of  transverse  section  through  rabbit  embryo.     (After   Keith.) 


the  duct  of  Cuvier  (Figs.  54,  55).    The  front  part  of  this  ridge  grows  across  and 
obliterates  the  pleuro-pericardial  opening;  the  hinder  part  grows  across  the  pleuro- 

1^    peritoneal  opening. 
■        With  the  continued  growth  of  the  lungs  the  pleural  cavities  are  pushed  forward 
ki 


74 


EMBRYOLOGY 


in  the  body-wall  toward  the  ventral  median  line,  thus  separating  the  pericardium 
from  the  lateral  thoracic  walls  (Fig.  53) .  The  further  development  of  the  peritoneal 
cavity  has  been  described  with  the  development  of  the  digestive  tube  (page  168 
et  seq.). 


Spken 

Colon 
Suprarenal  gland 
Eleventh  rib 
Twelfth  rib 


Sternn-costal part  of 
Diaphragma 
Central  tendon  of  Diaphragma 
Inferioi-  vena  cava 

(Esophagus 

Vertebral  part  of  Diaphragma 
T  Posterior  mediastinal  cavity 
-Aorta 


—  Spino-costal  hiattis 


Left  pleura 


Eight  pleura 


Fig.  57. — The  thoracic  aspect  of  the  diaphragm  of  a  newly  born  child  in  which  the  communication  between  the 
peritoneum  and  pleura  haa  not  been  closed  on  the  left  side;  the  position  of  the  opening  is  marked  on  the  right  side  by 
the  spinocostal  hiatus.     (After  Keith.) 


THE  FORM  OF  THE  EMBRYO  AT  DIFFERENT  STAGES  OF  ITS  GROWTH. 

First  Week. — During  this  period  the  ovum  is  in  the  uterine  tube.  Having  been  fertilized  in 
the  upper  part  of  the  tube,  it  slowly  passes  down,  undergoing  segmentation,  and  reaches  the 
uterus.  Peters^  described  a  specimen,  the  age  of  which  he  reckoned  as  from  three  to  four  days. 
It  was  imbedded  in  the  decidua  on  the  posterior  wall  of  the  uterus  and  enveloped  by  a  decidua 
capsularis,  the  central  part  of  which,  however,  consisted  merely  of  a  layer  of  fibrin.  The  ovum 
was  in  the  form  of  a  sac,  the  outer  wall  of  which  consisted  of  a  layer  of  trophoblast;  inside  this 


Heart 


Amnion 


Fig.  58.- 


Body-stalk 


Chorion 
-Human  embryo  about  fifteen  days  old. 


(His.) 


was  a  thin  layer  of  mesoderm  composed  of  round,  oval,  and  spindle-shaped  cells.  Numerous 
villous  processes — some  consisting  of  trophoblast  only,  others  possessing  a  core  of  mesoderm — 
projected  from  the  surface  of  the  ovum  into  the  surrounding  decidua.  Inside  this  sac  the  rudi- 
ment of  the  embryo  was  found  in  the  form  of  a  patch  of  ectoderm,  covered  by  a  small  but  com- 


'  Die  Einbettung  des  menschlichen  Eies,  1899. 


M 


WRM  OF  THE  EMBRYO  AT  DIFFERENT  STAGES  OF  ITS  GROWTH    75 


pletely  closed  amnion.    It  possessed  a  minute  yolk-sac  and  was  surroimded  by  mesoderm,  which 
was  connected  by  a  band  to  that  lining  the  trophoblast  (Fig.  32).^ 

Second  Week. — By  the  end  of  this  week  the  ovum  has  increased  considerably  in  size,  and  the 
majority  of  its  villi  are  vascularized.  The  embryo  has  assumed  a  definite  form,  and  its  cephaUc 
and  caudal  extremities  are  easily  distinguished.    The  neural  folds  are  partly  united.    The  embryo 


Mid-brain 


Fore-brain 
Stomodeum 
Mandibular  arch 
Heart 


Hind-brain 

Auditory  vesicle 


Amnion  {cut) 


Body-stalk 
Fig.  59. — Human  embryo  between  eighteen  and  twenty-one  days  old.      (His. 

more  completely  separated,  from  the  yolk-sac,  and  the  paraxial  mesoderm  is  being  divided  into 
Jthe  primitive  segments  (Fig.  58). 

Third  Week. — By  the  end  of  the  third  week  the  embryo  is  strongly  curved,  and  the  primitive 
segments  number  about  thirty.     The  primary  divisions  of  the  brain  are  visible,  and  the  optic 


Heart 


Fore-limb 


ki 


Byoid  arch 

Mandibular  arch 
Maxillary  process 

Eye-i 
Olfactory  pit 


Chorion' 

Hind-limb 

Fig.  60. — Human  embryo,  twenty-seven  to  thirty  days  old.     (His.) 

and  auditory  vesicles  are  formed.  Four  branchial  grooves  are  present:  the  stomodeum  is  well- 
marked,  and  the  bucco-pharyngeal  membrane  has  disappeared.  The  rudiments  of  the  hmba 
are  seen  as  short  buds,  and  the  Wolffian  bodies  are  visible  (Fig.  59). 

■  Br>-ce  and  Teacher  {Early  Deielopment  and  Imbedding  of  the  Human  Ovum,  1908)  have  described  an  ovum  which 
they  regard  as  thirteen  to  fourteen  days  old.  In  it  the  two  vesicles,  the  amnion  and  yolk-sac,  were  pre.sent,  but  there 
was  no  trace  of  a  layer  of  embryonic  ectoderm.  They  are  of  opinion  that  the  age  of  Peters'  ovum  has  been  understated, 
and  estimate  it  as  between  thirteen  and  one-half  and  fourteen  and  one-half  days. 


f  was  no  trace  < 

■^>  and  estimate 


76 


EMBRYOLOGY 


Fourth  Week. — The  embryo  is  markedly  curved  on  itself,  and  when  viewed  in  profile  is  almost 
circular  in  outline.  The  cerebral  hemispheres  appear  as  hollow  buds,  and  the  elevations  whica 
form  the  rudiments  of  the  auricula  are  visible.  The  limbs  now  appear  as  oval  flattened  projec- 
tions (Fig.  60). 

Heart 


I 


Hyoid 
Mandibular  arch 
Maxillary  process 
Eye 


limb 


Hind-limb 
Fig.  61. — Human  embryo,  thirty-one  to  thirty-four  days  old.     (His.) 

Fifth  Week. — The  embryo  is  less  curved  and  the  head  is  relatively  of  large  size.  DifTerentiation 
of  the  limbs  into  their  segments  occurs.  The  nose  forms  a  short,  flattened  projection.  The  cloaca! 
tubercle  is  evident  (Fig.  61). 


Auricula 


Fore-limb 


Hind-limb 


Umbilical  cord 


Fio.  62. — Human  embryo  of  about  six  weeks. 
(His.) 


Fio.  63. — Human  embryo  about  eight  and  a  half 
weeks  old.     (His.) 


Sixth  Week. — The  curvature  of  the  embryo  is  further  diminished.  The  branchial  grooves— 
except  the  first — have  disappeared,  and  the  rudiments  of  the  fingers  and  toes  can  be  recognized 
(Fig.  62). 

Seventh  and  Eighth  Weeks. — The  flexure  of  the  head  is  gradually  reduced  and  the  neck  is 
somewhat  lengthened.    The  upper  lip  is  completed  and  the  nose  is  more  prominent.    The  nostrils 


I 


FORM  OF  THE  EMBRYO  AT  DIFFERENT  STAGES  OF  ITS  GROWTH       77 


are  directed  forward  and  the  palate  is  not  completely  developed.  The  eyelids  are  present  in  the 
shape  of  folds  above  and  below  the  eye,  and 'the  different  parts  of  the  auricula  are  distinguish- 
able.   By  the  end  of  the  second  month  the  fetus  measures  from  28  to  30  mm.  in  length  (Fig.  63). 

Third  Month. — The  head  is  extended  and  the  neck  is  lengthened.  The  eyelids  meet  and  fuse, 
remaining  closed  until  the  end  of  the  sixth  month.  The  limbs  are  well-developed  and  nails  appear 
on  the  digits.  The  external  generative  organs  are  so  far  differentiated  that  it  is  possible  to  dis- 
tinguish the  sex.  By  the  end  of  this  month  the  length  of  the  fetus  is  about  7  cm.,  but  if  the  legs 
be  included  it  is  from  9  to  10  cm. 

Fourth  Month. — The  loop  of  gut  which  projected  into  the  umbilical  cord  is  withdrawn  within 
the  fetus.  The  hairs  begin  to  make  their  appearance.  There  is  a  general  increase  in  size  so  that 
by  the  end  of  the  fourth  month  the  fetus  is  from  12  to  13  cm.  in  length,  but  if  the  legs  be  included 
it  is  from  16  to  20  cm. 

Fifth  Month. — It  is  during  this  month  that  the  first  movements  of  the  fetus  are  usually  ob- 
Berved     The  eruption  of  hair  on  the  head  commences,  and  the  vemix  caseosa  begins  to  be  deposited. 

I  By  the  end  of  this  month  the  total  length  of  the  fetus,  including  the  legs,  is  from  25  to  27  cm 
J    Sixth  Month. — The  body  is  covered  by  fine  hairs  (lanugo)  and  the  deposit  of  vernix  caseosa 
Is  considerable.     The  papillae  of  the  skin  are  developed  and  the  free  border  of  the  nail  projects 
from  the  corium  of  the  dermis.      Measured  from  vertex  to  heels,  the  total  length  of  the  fetus 
at  the  end  of  this  month  is  from  30  to  32  cm. 

Seventh  Month. — The  pupillary  membrane  atrophies  and  the  eyehds  are  open.  The  testis 
descends  with  the  vaginal  sac  of  the  peritoneum.  From  vertex  to  heels  the  total  length  at  the 
end  of  the  seventh  month  is  from  35  to  36  cm.    The  weight  is  a  little  over  three  pounds. 

Eighth  Month. — The  skin  assumes  a  pink  color  and  is  now  entirely  coated  with  vemix  caseosa, 
and  the  lanugo  begins  to  disappear.  Subcutaneous  fat  has  been  developed  to  a  considerable 
extent,  and  the  fetus  presents  a  plump  appearance.  The  total  length,  i.  e.,  from  head  to  heels, 
at  the  end  of  the  eighth  month  is  about  40  cm.,  and  the  weight  varies  between  four  and  one-half 
and  five  and  one-half  pounds. 

Ninth  Month. — The  lanugo  has  largely  disappeared  from  the  trunk.  The  umbilicus  is  almost 
in  the  middle  of  the  body  and  the  testes  are  in  the  scrotum.  At  full  time  the  fetus  weighs  from 
aix  and  one-half  to  eight  poimds,  and  measures  from  head  to  heels  about  50  cm. 


Il 


BIBLIOGRAPHY. 


I 


Broman:     Normale  und  abnorme  Entwicklung  des  Menschen,  1911. 

Bryce,  Teacher  and  Kerr:    Contributions  to  the  Study  of  the  Early  Development  and 
Imbedding  of  the  Human  Ovum,  1908. 

Hertwig,  O.:     Handbuch   der  Vergleichenden  und  ExperimenteUen  Entwicklungslehre  der 
Wirbeltiere,  1906. 

His,  W.  :     Anatomie  menschlicher  Embryonen,  1880-1885. 
•  Hochstetter,  F.:     Bil der  der  ausserenKoperformeiniger  menschlicher  Embryonen  aus  den 
beiden  ersten  Monaten  der  Entwicklung,  1907. 

Keibel  and  Elze:     Normentafel  zur  Entwicklimgsgeschichte  des  Menschen,  1908. 

Keibel  and  Mall:     Manual  of  Human  Embryology,  1910-1912. 

KoLLMANN,  J.:     Handatlas  der  Entwicklimgsgeschichte  des  Menschen,  1907. 

tKoLLMANN,  J.:     Lehrbuch  der  Entwicklungsgeschichte  des  Menschen,  1898. 
Mall:     Contribution  to  the  Study  of  the  Pathology  of  the  Human  Embryo,  Jour,  of  Morph., 
908.    See  also  contributions  to  Embryology  of  the  Carnegie  Institution  of  Washington. 
Mall:     Development  of  the  Human  Coelom,  Jour,  of  Morph.,  1897. 

Peters,  H.:    Ueber  die  Einbettung  des  menschlichen  Eies  und  das  frviheste  bisher  bekannte 
menschliche  Placentationsstadium,  1899. 


OSTEOLOGY. 


^ 


rriHE  general  framework  of  the  body  is  built  up  mainh'  of  a  series  of  bones, 
-'-  supplemented,  however,  in  certain  regions  by  pieces  of  cartilage;  the  bony 
part  of  the  framework  constitutes  the  skeleton. 

In  the  skeleton  of  the  adult  there  are  206  distinct  bones,  as  follows: — 


Axial 
Skeleton 


Appendicular 
Skeleton 


Vertebral  column 
Skull    .... 
Hyoid  bone    . 
Ribs  and  sternum 


f  Upper  extremities 
\  Lower  extremities 


Auditory  ossicles 


^ 


Total 


26 

22 

1 

25 

—  74 
64 

62 

—  126 

6 

206 


The  patellse  are  included  in  this  enumeration,  but  the  smaller  sesamoid  bones 
are  not  reckoned. 

Bones  are  divisible  into  four  classes:  Long,  Short,  Flat,  and  Irregular, 
Long  Bones. — The  long  bones  are  found  in  the  limbs,  and  each  consists  of  a  body 
or  shaft  and  two  extremities.  The  body,  or  diaphysis  is  cylindrical,  with  a  central 
cavity  termed  the  medullary  canal;  the  ^all  consists  of  dense,  compact  tissue 
of  considerable  thickness  in  the  middle  part  of  the  body,  but  becoming  thinner 
toward  the  extremities;  within  the  medullary  canal  is  some  cancellous  tissue, 
scanty  in  the  middle  of  the  body  but  greater  in  amount  toward  the  ends.  The 
extremities  are  generally  expanded,  for  the  purposes  of  articulation  and  to  afford 
broad  surfaces  for  muscular  attachment.  They  are  usually  developed  from  sep- 
arate centers  of  ossification  termed  epiphyses,  and  consist  of  cancellous  tissue 
surrounded  by  thin  compact  bone.  The  medullary  canal  and  the  spaces  in  the 
cancellous  tissue  are  filled  with  marrow.  The  long  bones  are  not  straight,  but 
curved,  the  curve  generally  taking  place  in  two  planes,  thus  affording  greater 
strength  to  the  bone.  The  bones  belonging  to  this  class  are:  the  clavicle,  humerus, 
radius,  ulna,  femur,  tibia,  fibula,  metacarpals,  metatarsals,  and  phalanges. 

Short  Bones. — Where  a  part  of  the  skeleton  is  intended  for  strength  and  com- 
pactness combined  with  limited  movement,  it  is  constructed  of  a  number  of  short 
bones,  as  in  the  carpus  and  tarsus.  These  consist  of  cancellous  tissue  covered 
by  a  thin  crust  of  compact  substance.     The  patellae,  together  with  the  other 

.  sesamoid  bones,  are  by  some  regarded  as  short  bones. 

Flat  Bones. — Where  the  principal  requirement  is  either  extensive  protection  or 
the  provision  of  broad  surfaces  for  muscular  attachment,  the  bones  are  expanded 
into  broad,  flat  plates,  as  in  the  skull  and  the  scapula.    These  bones  are  composed 

^  of  two  thin  layers  of  compact  tissue  enclosing  between  them  a  variable  quantity 
of  cancellous  tissue.    In  the  cranial  bones,  the  layers  of  compact  tissue  are  famili- 

\  arly  known  as  the  tables  of  the  skull;  the  outer  one  is  thick  and  tough;  the  inner 
is  thin,  dense,  and  brittle,  and  hence  is  termed  the  vitreous  table.    The  intervening 

(79) 


JTEOLOGY 


I 


I 


cancellous  tissue  is  called  the  diploe,  and  this,  in  certain  regions  of  the  skull, 
becomes  absorbed  so  as  to  leave  spaces  filled  with  air  (air-sinuses)  between 
the  two  tables.  The  flat  bones  are:  the  occipital,  parietal,  frontal,  nasal,  lacrimal, 
vomer,  scapula,  os  coxae  {Jiip  hone),  sternum,  ribs,  and,  according  to  some,  tht- 
patella. 

Irregular  Bones. — The  irregular  bones  are  such  as,  from  their  peculiar  form] 
cannot  be  grouped  under  the  preceding  heads.  They  consist  of  cancellous  tissue 
enclosed  within  a  thin  layer  of  compact  bone.  The  irregular  bones  are:  the 
vertebrae,  sacrum,  coccjrx,  temporal,  sphenoid,  ethmoid,  zygomatic,  maxilla,  mandible, 
palatine,  inferior  nasal  concha,  and  hyoid.  _d^m 

Surfaces  of  Bones. — If  the  surface  of  a  bone  be  examined,  certain  eminence^iJH 
and  depressions  are  seen.  These  eminences  and  depressions  are  of  two  kinds:  ' 
articular  and  non-articular.  Well-marked  examples  of  articular  eminences  are 
found  in  the  heads  of  the  humerus  and  femur;  and  of  articular  depressions  in  the 
glenoid  cavity  of  the  scapula,  and  the  acetabulum  of  the  hip  bone.  Non-articular 
eminences  are  designated  according  to  their  form.  Thus,  a  broad,  rough,  uneven 
elevation  is  called  a  tuberosity,'  protuberance,  or  process,  a  small,  rough  prominence, 
a  tubercle ;  a  sharp,  slender  pointed  eminence,  a  spine ;  a  narrow,  rough  elevation, 
running  some  way  along  the  surface,  a  ridge,  crest,  or  line.  Non-articular  depres- 
sions are  also  of  variable  form,  and  are  described  as  fossae,  pits,  depressions,  grooves, 
furrows,  fissures,  notches,  etc.  These  non-articular  eminences  and  depressions  serve 
to  increase  the  extent  of  surface  for  the  attachment  of  ligaments  and  muscles,  and 
are  usually  well-marked  in  proportion  to  the  muscularity  of  the  subject.  A  short 
perforation  is  called  a  foramen,  a  longer  passage  a  canal. 

DEVELOPMENT  OF  THE  SKELETON. 

The  Skeleton. — The  skeleton  is  of  mesodermal  origin,  and  may  be  divided  into 
(a)  that  of  the  trunk  (axial  skeleton),  comprising  the  vertebral  column,  skull,  ribs, 
and  sternum,  and  (6)  that  of  the  limbs  (appendicular  skeleton). 

The  Vertebral  Column.- — The  notochord  (Fig.  19)  is  a  temporary  structure  and 
forms  a  central  axis,  around  which  the  segments  of  the  vertebral  column  are  devel- 
oped.^ It  is  derived  from  the  entoderm,  and  consists  of  a  rod  of  cells,  which  lies 
on  the  ventral  aspect  of  the  neural  tube  and  reaches  from  the  anterior  end  of  the 
mid-brain  to  the  extremity  of  the  tail.  On  either  side  of  it  is  a  column  of  paraxial 
mesoderm  which  becomes  subdivided  into  a  number  of  more  or  less  cubical  seg- 
ments, the  primitive  segments  (Figs.  19  and  20).  These  are  separated  from  one 
another  by  intersegmental  septa  and  are  arranged  symmetrically  on  either  side  of 
the  neural  tube  and  notochord:  to  every  segment  a  spinal  nerve  is  distributed. 
At  first  each  segment  contains  a  central  cavity,  the  myoccEl,  but  this  is  soon  filled 
■with  a  core  of  angular  and  spindle-shaped  cells.  The  cells  of  the  segment  become 
differentiated  into  three  groups,  which  form  respectively  the  cutis-plate  or  derma- 
tome, the  muscle-plate  or  myotome,  and  the  sclerotome  (Fig.  64).  The  cutis-plate 
is  placed  on  the  lateral  and  dorsal  aspect  of  the  myoccel,  and  from  it  the  true  skin 
of  the  corresponding  segment  is  derived ;  the  muscle-plate  is  situated  on  the  medial 
side  of  the  cutis-plate  and  furnishes  the  muscles  of  the  segment.  The  cells  of  the 
sclerotome  are  largely  derived  from  those  forming  the  core  of  the  myocoel,  and  lie 
next  the  notochord.  Fusion  of  the  individual  sclerotomes  in  an  antero-posterior 
direction  soon  takes  place,  and  thus  a  continuous  strand  of  cells,  the  sclerotogenous 
layer,  is  formed  along  the  ventro-lateral  aspects  of  the  neural  tube.  The  cells  of 
this  layer  proliferate  rapidly,  and  extending  medialward  surround  the  notochord; 
at  the  same  time  they  grow  backward  on  the  lateral  aspects  of  the  neural  tube 
and  eventually  surround  it,  and  thus  the  notochord  and  neural  tube  are  enveloped 

'  In  the  amphioxus  the  notochord  persists  and  forms  the  only  representative  of  a  skeleton  in  that  animal. 


DEVELOPMENT  OF  THE  SKELETON 


81 


i 

I 


by  a  continuous  sheath  of  mesoderm,  which  is  termed  the  membranous  vertebral 
column.  In  this  mesoderm  the  original  segments  are  still  distinguishable,  but  each 
is  now  differentiated  into 
two  portions,  an  anterior, 
consisting  of  loosely  arranged 
cells,  and  a  posterior,  of 
more  condensed  tissue  (Fig. 
65,  A  and  B) .  Between  the 
two  portions  the  rudiment 
of  the  intervertebral  fibro- 
cartilage  is  laid  down  (Fig. 
65,  C).  Cells  from  the  pos- 
terior mass  grow  into  the 
intervals  between  the  myo- 
tomes (Fig.  65,  B  and  C)  of 
the  corresponding  and  suc- 
ceeding segments,  and  extend 
both  dorsally  and  ventrally; 
the  dorsal  extensions  sur- 
round the  neural  tube  and 
represent  the  future  verte- 
bral arch,  while  the  ventral 
extend  into  the  body-wall 
as  the  costal  processes.  The 
hinder  part  of  the  posterior 
mass  joins  the  anterior  mass 
of  the  succeeding  segment 
to  form  the  vertebral  body. 
Each  vertebral  body  is  there- 
fore a  composite  of  two  segments,  being  formed  from  the  posterior  portion  of 
one  segment  and  the  anterior  part  of  that  immediately  behind  it.    The  vertebral 


Fio.  64. — Transverse  section  of  a  human  embryo  of  the  third  week 
to  show  the  dififerentiation  of  the  primitive  segment.  (Kollmann.)  ao. 
Aorta.  m.p.  Muscle-plate,  n.c.  Neural  canal,  sc.  Sclerotome,  s  p. 
cutis-plate. 


Myotome 


Anterior  portion  of  sclerotome 
Notochord 

Posterior  portion  of  sclerotome. 
Intermyolomic  septum 
Costal  process 


'?\ 


Ml  it 


Intervertebral 
fibrocartilage 

Notochord 


Centr 


ISJiii; 


iv;:j 


::*.:: 


m^ 


"tiiiVrr?) 


;;;:: 


/tUli»4i.«»'»«jL      AV.  ••«.... I. i.\ 


/1 1 1  •  I  i  r:  t  r : !!  J  V,  1 '  >?••.".'.*.♦•  i  •  •  u  j  » 
(., . .'. « .V.V,\ .•; \\  I  /•.•:;.v/....;.'.,<3 


B 


FiQ.  65. — Scheme  showing  the  manner  in  which  each  vertebral  centrum  is  developed  from  portions  of  two  adjacent 

segments. 


I 


and  costal  arches  are  derivatives  of  the  posterior  part  of  the  segment  in  front 
of  the  intersegmental  septum  with  which  they  are  associated. 
6 


OSTEOLOGY 


I 


This  stage  is  succeeded  by  that  of  the  cartilaginous  vertebral  column.     In  the 
fourth  week  two  cartilaginous  centers  make  their  appearance,  one  on  either  side  o^^ 
the  notochord;  these  extend  around  the  notochord  and  form  the  body  of  the  cartil-^U 
aginous  vertebra.    A  second  pair  of  cartilaginous  foci  appear  in  the  lateral  parts  of 
the  vertebral  bow,  and  grow  backward  on  either  side  of  the  neural  tube  to  form  ^  ,_ 
the  cartilaginous  vertebral  arch,  and  a  separate  cartilaginous  center  appears  foilMfl 
each  costal  process.    By  the  eighth  week  the  cartilaginous  arch  has  fused  with  the 
body,  and  in  the  fourth  month  the  two  halves  of  the  arch  are  joined  on  the  dorsal 
aspect  of  the  neural  tube.    The  spinous  process  is  developed  from  the  junction  of 
the  two  halves  of  the  vertebral  arch.    The  transverse  process  grows  out  from  the, 
vertebral  arch  behind  the  costal  process. 

In  the  upper  cervical  vertebrae  a  band  of  mesodermal  tissue  connects  the  ends  of 
the  vertebral  arches  across  the  ventral  surfaces  of  the  intervertebral  fibrocartilages. 
This  is  termed  the  hypochordal  bar  or  brace;  in  all  except  the  first  it  is  transitory 
and  disappears  by  fusing  with  the  fibrocartilages.  In  the  atlas,  however,  the  entire 
bow  persists  and  undergoes  chondrification;  it  develops  into  the  anterior  arch  of  the 
bone,  while  the  cartilage  representing  the  body  of  the  atlas  forms  the  dens  or 
odontoid  process  which  fuses  with  the  bod}^  of  the  second  cervical  vertebra. 


Anterior 

longitudiiial 

ligamevt 


Posterior  lo7igiludinal 

ligament 
Cartilaginous  end 

of  vertebral  body 

Nucleus  puljmsus 

Intervertebral  fibro- 
cartilage 

Slight  enlargement 
of  notochord  in 
the  cartilaginous 
vertebral  body 


Fig.  66. — Sagittal  section  through  an  intervertebral  fibrocartilage  and  adjacent  parts  of  two  vertebrae  of  an  advanced 

sheep's  embryo.     (KoUiker.) 

The  portions  of  the  notochord  which  are  surrounded  by  the  bodies  of  the  verte- 
brae atrophy,  and  ultimately  disappear,  while  those  which  lie  in  the  centers  of  the 
intervertebral  fibrocartilages  undergo  enlargement,  and  persist  throughout  life  as 
the  central  nucleus  pulposus  of  the  fibrocartilages  (Fig.  66). 

The  Ribs. — The  ribs  are  formed  from  the  ventral  or  costal  processes  of  the 
primitive  vertebral  bows,  the  processes  extending  between  the  muscle-plates.  In 
the  thoracic  region  of  the  vertebral  column  the  costal  processes  grow  lateralward  to 
form  a  series  of  arches,  the  primitive  costal  arches.  As  already  described,  the 
transverse  process  grows  out  behind  the  vertebral  end  of  each  arch.  It  is  at  first 
connected  to  the  costal  process  by  continuous  mesoderm,  but  this  becomes  differ- 
entiated later  to  form  the  costotransverse  ligament;  between  the  costal  process 
and  the  tip  of  the  transverse  process  the  costotransverse  joint  is  formed  by 
absorption.  The  costal  process  becomes  separated  from  the  vertebral  bow  by  the 
development  of  the  costocentral  joint.  In  the  cervical  vertebroB  (Fig.  67)  the  trans- 
verse process  forms  the  posterior  boundary  of  the  foramen  transversarium,  while 
the  costal  process  corresponding  to  the  head  and  neck  of  the  rib  fuses  with  the 


I 


DEVELOPMENT  OF  THE  SKELETON 


83 


body  of  the  vertebra,  and  forms  the  antero-lateral  boundary  of  the  foramen.  The 
distal  portions  of  the  primitive  costal  arches  remain  undeveloped;  occasionally 
the  arch  of  the  seventh  cervical  vertebra  undergoes  greater  development,  and  by 
the  formation  of  costovertebral  joints  is  separated  off  as  a  rib.  In  the  lumbar 
region  the  distal  portions  of  the  primitive  costal  arches  fail ;  the  proximal  portions 
fuse  with  the  transverse  processes  to  form  the  transverse  processes  of  descriptive 
anatomy.  Occasionally  a  movable  rib  is  developed  in  connection  with  the  first 
lumbar  vertebra.  In  the  sacral  region  costal  processes  are  developed  only  in 
connection  with  the  upper  three,  or  it  may  be  four,  vertebrae;  the  processes  of 
adjacent  segments  fuse  with  one  another  to  form  the  lateral  parts  of  the  sacrum. 
The  coccygeal  vertebrcs  are  devoid  of  costal  processes. 


CERVICAL 


LUMBAR 


THORACIC 


SACRAL 


I 


Fig.  67. — Diagrams  showing  the  portions  of  the  adult  vertebrse  derived  respectively  from  the  bodies,  vertebral 
arches,  and  costal  processes  of  the  embrj'onic  vertebrse.  The  bodies  are  represented  in  yellow,  the  vertebral  arches 
in  red,  and  the  costal  processes  in  blue. 

The  Sternum. — The  ventral  ends  of  the  ribs  become  united  to  one  another  by  a 
longitudinal  bar  termed  the  sternal  plate,  and  opposite  the  first  seven  pairs  of  ribs 
these  sternal  plates  fuse  in  the  middle  line  to  form  the  manubrium  and  body  of  the 
sternum.  The  xiphoid  process  is  formed  by  a  backward  extension  of  the  sternal 
plates. 

The  Skull. — Up  to  a  certain  stage  the  development  of  the  skull  corresponds  with 
that  of  the  vertebral  column;  but  it  is  modified  later  in  association  with  the  expan- 
sion of  the  brain-vesicles,  the  formation  of  the  organs  of  smell,  sight,  and  hearing, 
and  the  development  of  the  mouth  and  pharynx. 


84 


OSTEOLOGY 


I 


Fossa 
hypophyseos 


Mesoderm  of  base 
of  skull 


Parachordal 
cartilage 


The  notochord  extends  as  far  forward  as  the  anterior  end  of  the  mid-brain,  and 
becomes  partly  surrounded  by  mesoderm  (Fig.  68) .  The  posterior  part  of  this  meso- 
dermal investment  corresponds  with  the  basilar  part  of  the  occipital  bone,  and  show  s 
a  subdivision  into  four  segments,  which  are  separated  by  the  roots  of  the  hypo- 
glossal nerve.    The  mesoderm  then  extends  over  the  brain-vesicles,  and  thus  the 

entire  brain  is  enclosed  by  a  mesodermal 
investment,  which  is  termed  the  membran- 
ous cranium.  From  the  inner  layer  of  this 
the  bones  of  the  skull  and  the  membranes 
of  the  brain  are  developed ;  from  the  outer 
laj^er  the  muscles,  bloodvessels,  true  skin, 
and  subcutaneous  tissues  of  the  scalp.  In 
the  shark  and  dog-fish  this  membranous 
cranium  undergoes  complete  chondrifi- 
cation,  and  forms  the  cartilaginous  skull 
or  chondrocranium  of  these  animals.  In 
mammals,  on  the  other  hand,  the  process 
of  chondrification  is  limited  to  the  base 
of  the  skull — ^the  roof  and  sides  being 
covered  in  by  membrane.  Thus  the  bones 
of  the  base  of  the  skull  are  preceded  by 
cartilage,  those  of  the  roof  and  sides 
by  membrane.  The  posterior  part  of  the 
base  of  the  skull  is  developed  around 
the  notochord,  and  exhibits  a  segmented 
condition  analogous  to  that  of  the  vertebral  column,  while  the  anterior  part  arises 
in  front  of  the  notochord  and  shows  no  regular  segmentation.  The  base  of  the  skull 
may  therefore  be  divided  into  (a)  a  chordal  or  vertebral,  and  (b)  a  prechordal  or 
prevertebral  portion. 

SitvMion  of  olfactory  pit     Ethmoid  plate 

and  nasal    Olfactory  organ 


Anterior  arch  of  atlas 

Notochord 

Body  of  axis 

Third  cervical 
vertebra 


Fio.  68. — Sagittal  section  of  ceplialic   end  ot 
chord.    (Keibel.) 


Fossa 
hypophyseos 


Trabecvla 
cranii 

SitvMion  of 

avditory 

vesicle 

Parachordal 

cartilage 

Notochord 


Extension  around 
7       olfactory  organ 
Foramina  for 
olfactory  nerves 

.  Eyeball 

Fossa 
~  hypophyseos 


—  Basilar  plate 
--Auditory  vesicle 

•Notochord 


Fig.  69. — Diagrams  of  the  cartilaginous  cranium.     (Wiedersheim. 

In  the  lower  vertebrates  two  pairs  of  cartilages  are  developed,  viz.,  a  pair  of 
parachordal  cartilages,  one  on  either  side  of  the  notochord;  and  a  pair  of  pre- 
chordal cartilages,  the  trabeculse  cranii,  in  front  of  the  notochord  (Fig.  66).  The 
parachordal  cartilages  (Fig.  69)  unite  to  form  a  basilar  plate,  from  which  the  car- 
tilaginous part  of  the  occipital  bone  and  the  basi-sphenoid  are  developed.  On  the 
lateral  aspects  of  the  parachordal  cartilages  the  auditory  vesicles  are  situated, 


I 


DEVELOPMENT  OF  THE  SKELETON 


85 


and  the  mesoderm  enclosing  them  is  soon  converted  into  cartilage,  forming  the 
cartilaginous  ear-capsules.  These  cartilaginous  ear-capsules,  which  are  of  an  oval 
shape,  fuse  with  the  sides  of  the  basilar  plate,  and  from  them  arise  the  petrous 
and  mastoid  portions  of  the  temporal  bones.  The  trabeculse  cranii  (Fig.  69)  are 
two  curved  bars  of  cartilage  which  embrace  the  hypophysis  cerebri;  their  posterior 
ends  soon  unite  with  the  basilar  plate,  while  their  anterior  ends  join  to  form  the 
ethmoidal  plate,  which  extends  forward  between  the  fore-brain  and  the  olfactory 
pits.    Later  the  trabeculse  meet  and  fuse  below  the  hypophysis,  forming  the  floor 


Crista  gain 


Cribriform  plate 


Meckel's  cartilage 
Malleus 
I71CUS 

Jnt.  acoustic  meat. 
Jugular  foramen 
Tossa  svbarcuata 


janal  for  hypoglossal  nerve 


Small  wing  of  sphenoid 
Optic  foramen 


-Great  wing  of 

sphenoid 

Sella  turcica 

Dorsum  seUce 


Canal  for  facial 
nerve 

Ear  capsule 
Ihictus  endal. 


Foramen  magnum 


FiQ.  70. — Model  of  the  chondrocranium  of  a  human  embryo,  8  cm.  long. 

not  represented. 


(Hertwig.)      The  membrane  bones  are 


of  the  fossa  hypophyseos  and  so  cutting  off  the  anterior  lobe  of  the  hypophysis 
from  the  stomodeum.  The  median  part  of  the  ethmoidal  plate  forms  the  bony 
and  cartilaginous  parts  of  the  nasal  septum.  From  the  lateral  margins  of  the 
trabeculse  cranii  three  processes  grow  out  on  either  side.  The  anterior  forms  the 
ethmoidal  labyrinth  and  the  lateral  and  alar  cartilages  of  the  nose;  the  middle 
gives  rise  to  the  small  wing  of  the  sphenoid,  while  from  the  posterior  the  great 
wing  and  lateral  pterygoid  plate  of  the  sphenoid  are  developed  (Figs.  70,  71). 
The  bones  of  the  vault  are  of  membranous  formation,  and  are  termed  dermal  or 
covering  bones.    They  are  partly  developed  from  the  mesoderm  of  the  membranous 


OSTEOLOGY 


I 


cranium,  and  partly  from  that  which  lies  outside  the  entoderm  of  the  fore- 
gut.  They  comprise  the  upper  part  of  the  occipital  squama  (interparietal),  th(^ 
squamse  and  tympanic  parts  of  the  temporals,  the  parietals,  the  frontal,  the  vomer, 
the  medial  pterygoid  plates,  and  the  bones  of  the  face.  Some  of  them  remain 
distinct  throughout  life,  e.  g.,  parietal  and  frontal,  while  others  join  with  the  bones 
of  the  chondrocranium,  e.  g.,  interparietal,  squamae  of  temporals,  and  medial 
pterygoid  plates. 

Recent  observations  have  shown  that,  in  mammals,  the  basi-cranial  cartilage, 
both  in  the  chordal  and  prechordal  regions  of  the  base  of  the  skull,  is  developed 
as  a  single  plate  which  extends  from  behind  forward.  In  man,  however,  its  posterior 
part  shows  an  indication  of  being  developed  from  two  chondrifying  centers  which 
fuse  rapidly  in  front  and  below.  The  anterior  and  posterior  thirds  of  the  cartilage 
surround  the  notochord,  but  its  middle  third  lies  on  the  dorsal  aspect  of  the  noto- 
chord,  which  in  this  region  is  placed  between  the  cartilage  and  the  wall  of  the 
pharynx. 


Optic  foramen    Small  wing  of  sphenoid 


Great  wing  of  sphenoid 


Nasal 
capsiUe 


Vomer 


Palattne 
bone 


Mandible 


Cricoid  cart. 

Thyroid  cart. 


Styloid  process 
Fen.  cochlew 


Canal  for  hypoglossal 

nerve 


Fio.  71. — The  same  model  as  shown  in  Fig.  70  from  the  left  side.    Certain  of  the  membrane  bones  of  the  right  side 

are  represented  in  yellow.     (Hertwig.) 


BONE 

Structure  and  Physical  Properties. — Bone  is  one  of  the  hardest  structures  of 
the  animal  body;  it  possesses  also  a  certain  degree  of  toughness  and  elasticity. 
Its  color,  in  a  fresh  state,  is  pinkish-white  externally,  and  deep  red  within.  On 
examining  a  section  of  any  bone,  it  is  seen  to  be  composed  of  two  kinds  of  tissue, 
one  of  which  is  dense  in  texture,  like  ivory,  and  is  termed  compact  tissue;  the  other 
consists  of  slender  fibers  and  lamellae,  which  join  to  form  a  reticular  structure; 
this,  from  its  resemblance  to  lattice-work,  is  called  cancellous  tissue.  The  compact 
tissue  is  always  placed  on  the  exterior  of  the  bone,  the  cancellous  in  the  interior. 
The  relative  quantity  of  these  two  kinds  of  tissue  varies  in  different  bones,  and 
in  different  parts  of  the  same  bone,  according  as  strength  or  lightness  is  requisite. 
Close  examination  of  the  compact  tissue  shows  it  to  be  extremely  porous,  so  that 
the  difference  in  structure  between  it  and  the  cancellous  tissue  depends  merely 
upon  the  different  amount  of  solid  matter,  and  the  size  and  number  of  spaces  in 
each;  the  cavities  are  small  in  the  compact  tissue  and  the  solid  matter  between 


I 


BONE 


87 


them  abundant,  while  in  the  cancellous  tissue  the  spaces  are  large  and  the  solid 
matter  is  in  smaller  quantity. 

Bone  during  life  is  permeated  by  vessels,  and  is  enclosed,  except  where  it  is 
coated  with  articular  cartilage,  in  a  fibrous  membrane,  the  periosteum,  by  means 
of  which  many  of  these  vessels  reach  the  hard  tissue.  If  the  periosteum  be  stripped 
from  the  surface  of  the  living  bone,  small  bleeding  points  are  seen  which  mark  the 
entrance  of  the  periosteal  vessels;  and  on  section  during  life  every  part  of  the 
bone  exudes  blood  from  the  minute  vessels  which  ramify  in  it.  The  interior  of 
each  of  the  long  bones  of  the  limbs  presents  a  cylindrical  cavity  filled  with  marrow 
and  lined  by  a  highly  vascular  areolar  structure,  called  the  medullary  membrane. 

The  Strength  of  Bone  Compared  with  other  Materials 


Substance. 


Weight  in 
pounds  per 
cubic  foot. 


Ultimate  strength. 
Pounds  per  square  inch. 


Tension. 


Compression. 


Shear. 


I 


Medium  steel 490  65,000  |      60,000 

Granite 170  1,500  15,000 

Oak,  white 46  12,500^  7,000^ 

Compact  bone  (low) 119  13,200^  18,000i 

Compact  bone  (high) I     i       17,700^  ;       24,000i 


40,000 
2,000 
4,0002 

11,800'' 
7,1601 


Periosteirai. — ^The  periosteum  adheres  to  the  surface  of  each  of  the  bones  in 
nearly  every  part,  but  not  to  cartilaginous  extremities.  When  strong  tendons  or 
ligaments  are  attached  to  a  bone,  the  periosteum  is  incorporated  with  them.  It 
consists  of  two  layers  closely  united  together,  the  outer  one  formed  chiefly  of 
connective  tissue,  containing  occasionally  a  few  fat  cells;  the  inner  one,  of  elastic 
fibers  of  the  finer  kind,  forming  dense  membranous  networks,  which  again  can  be 
separated  into  several  layers.  In  young  bones  the  periosteum  is  thick  and  very 
vascular,  and  is  intimately  connected  at  either  end  of  the  bone  with  the  epiphysial 
cartilage,  but  less  closely  with  the  body  of  the  bone,  from  which  it  is  separated  by 
a  layer  of  soft  tissue,  containing  a  number  of  granular  corpuscles  or  osteoblasts,  by 
which  ossification  proceeds  on  the  exterior  of  the  young  bone.  Later  in  life  the 
periosteum  is  thinner  and  less  vascular,  and  the  osteoblasts  are  converted  into  an 
epithelioid  layer  on  the  deep  surface  of  the  periosteum.  The  periosteum  serves 
as  a  nidus  for  the  ramification  of  the  vessels  previous  to  their  distribution  in  the 
bone;  hence  the  liability  of  bone  to  exfoliation  or  necrosis  when  denuded  of  this 
membrane  by  injury  or  disease.  Fine  nerves  and  lymphatics,  which  generally 
accompany  the  arteries,  may  also  be  demonstrated  in  the  periosteum. 

Marrow. — The  marrow  not  only  fills  up  the  cylindrical  cavities  in  the  bodies  of 
the  long  bones,  but  also  occupies  the  spaces  of  the  cancellous  tissue  and  extends 
into  the  larger  bony  canals  (Haversian  canals)  which  contain  the  bloodvessels. 
It  differs  in  composition  in  different  bones.  In  the  bodies  of  the  long  bones  the 
marrow  is  of  a  yellow  color,  and  contains,  in  100  parts,  96  of  fat,  1  of  areolar  tissue 
and  vessels,  and  3  of  fluid  with  extractive  matter;  it  consists  of  a  basis  of  connective 
tissue  supporting  numerous  bloodvessels  and  cells,  most  of  which  are  fat  cells 
but  some  are  "marrow  cells,"  such  as  occur  in  the  red  marrow  to  be  immediately 
described.  In  the  flat  and  short  bones,  in  the  articular  ends  of  the  long  bones, 
in  the  bodies  of  the  vertebrae,  in  the  cranial  diploe,  and  in  the  sternum  and  ribs 
the  marrow  is  of  a  red  color,  and  contains,  in  100  parts,  75  of  water,  and  25  of  solid 
matter  consisting  of  cell-globulin,  nucleoprotein,  extractives,  salts,  and  only  a 
small  proportion  of  fat.  The  red  marrow  consists  of  a  small  quantity  of  connective 
tissue,  bloodvessels,  and  numerous  cells  (Fig.  72),  some  few  of  which  are  fat  cells, 

1  Indicates  stresses  with  the  grain,  j.  e.,  when  the  load  is  parallel  to  the  long  axis  of  the  material,  or  parallel  to  the 
direction  of  the  fibers  of  the  material. 

2  Indicates  unit-stresses  across  the  grain,  i.  e.,  at  right  angles  to  the  direction  of  the  fibers  of  the  material. 


OSTEOLOGY 

but  the  great  majority  are  roundish  nucleated  cells,  the  true  "marrow  cells' 
of  Kolliker.  These  marrow  cells  proper,  or  myelocjrtes,  resemble  in  appearance' 
lymphoid  corpuscles,  and  like  them  are  ameboid;  they  generally  have  a  hyalin<j 
protoplasm,  though  some  show  granules  either  oxyphil  or  basophil  in  reaction. 
A  number  of  eosinophil  cells  are  also  present.  Among  the  marrow  cells  may  be 
seen  smaller  cells,  which  possess  a  slightly  pinkish  hue;  these  are  the  erythroblasts 
or  normoblasts,  from  which  the  red  corpuscles  of  the  adult  are  derived,  and  which 
may  be  regarded  as  descendants  of  the  nucleated  colored  corpuscles  of  the  embryo. 
Giant  cells  (myeloj^laxes,  osteoclasts),  large,  multinucleated,  protoplasmic  masses, 
are  also  to  be  found  in  both  sorts  of  adult  marrow,  but  more  particularly  in  red 
marrow.  They  were  believed  by  Kolliker  to  be  concerned  in  the  absorption  of 
bone  matrix,  and  hence  the  name  which  he  gave  to  them — osteoclasts.  They 
excavate  in  the  bone  small  shallow  pits  or  cavities,  which  are  named  Howship's 
foveolse,  and  in  these  they  are  found  lying. 


Normoblast  with  dividing  nucleus 


Myelocyte  • 


Erythrocyte  — '^^ 


Myeloplaxe  — '>- — 


Myelocyte ' 


Faf 


[__  Eosinophil 
cell 


11-  Normoblasts 

.L_  Myelocyte 
dividing 

"  Myelocyte 


FiQ.  72. — Human  bone  marrow.     Highly  magnified. 

Vessels  and  Nerves  of  Bone. — The  bloodvessels  of  bone  are  very  numerous.  Those 
of  the  compact  tissue  are  derived  from  a  close  and  dense  network  of  vessels  ramify- 
ing in  the  periosteum.  From  this  membrane  vessels  pass  into  the  minute  orifices 
in  the  compact  tissue,  and  run  through  the  canals  which  traverse  its  substance. 
The  cancellous  tissue  is  supplied  in  a  similar  way,  but  by  less  numerous  and  larger 
vessels,  which,  perforating  the  outer  compact  tissue,  are  distributed  to  the  cavities 
of  the  spongy  portion  of  the  bone.  In  the  long  bones,  numerous  apertures  may 
be  seen  at  the  ends  near  the  articular  surfaces;  some  of  these  give  passage  to  the 
arteries  of  the  larger  set  of  vessels  referred  to;  but  the  most  numerous  and  largest 
apertures  are  for  some  of  the  veins  of  the  cancellous  tissue,  which  emerge  apart 
from  the  arteries.  The  marrow  in  the  body  of  a  long  bone  is  supplied  by  one 
large  artery  (or  sometimes  more),  which  enters  the  bone  at  the  nutrient  foramen 
(situated  in  most  cases  near  the  center  of  the  body),  and  perforates  obliquely  the 
compact  structure.  The  medullary  or  nutrient  artery,  usually  accompanied  by  one 
or  two  veins,  sends  branches  upward  and  downward,  which  ramify  in  the  medul- 
lary membrane,  and  give  twigs  to  the  adjoining  canals.    The  ramifications  of  this 


I 


BONE 


89 


^ 


vessel  anastomose  with  the  arteries  of  the  cancellous  and  compact  tissues.  In  most 
of  the  flat,  and  in  many  of  the  short  spongy  bones,  one  or  more  large  apertures  are 
observed,  which  transmit  to  the  central  parts  of  the  bone  vessels  corresponding  to 
the  nutrient  arteries  and  veins.  The  veins  emerge  from  the  long  bones  in  three 
places  (Kolliker) :  (1)  one  or  two  large  veins  accompany  the  artery;  (2)  numerous 
large  and  small  veins  emerge  at  the  articular  extremities;  (3)  many  small  veins 
pass  out  of  the  compact  substance.  In  the  flat  cranial  bones  the  veins  are  large, 
very  numerous,  and  run  in  tortuous  canals  in  the  diploic  tissue,  the  sides  of  the 
canals  being  formed  by  thin  lamellae  of  bone,  perforated  here  and  there  for  the 
passage  of  branches  from  the  adjacent  cancelli.  The  same  condition  is  also 
found  in  all  cancellous  tissue,  the  veins  being  enclosed  and  supported  by  osseous 
material,  and  having  exceedingly  thin  coats.  When  a  bone  is  divided,  the  vessels 
remain  patulous,  and  do  not  contract  in  the  canals  in  which  they  are  contained. 
L3miphatic  vessels,  in  addition  to  those  found  in  the  periosteum,  have  been  traced 
by  Cruikshank  into  the  substance  of  bone,  and  Klein  describes  them  as  running  in 
the  Haversian  canals.  Nerves  are  distributed  freely  to  the  periosteum,  and  accom- 
pany the  nutrient  arteries  into  the  interior  of  the  bone.  They  are  said  by  Kolliker 
to  be  most  numerous  in  the  articular  extremities  of  the  long  bones,  in  the  vertebrae, 
and  in  the  larger  flat  bones. 


t 


Fig.  73. — Transverse  section  of  compact  tissue  bone.     Magnified.     (Sharpey.) 

Minute  Anatomy. — A  transverse  section  of  dense  bone  may  be  cut  with  a  saw 
and  ground  down  until  it  is  sufficiently  thin. 

If  this  be  examined  with  a  rather  low  power  the  bone  will  be  seen  to-be  mapped 
out  into  a  number  of  circular  districts  each  consisting  of  a  central  hole  surrounded 
by  a  number  of  concentric  rings.  These  districts  are  termed  Haversian  systems; 
the  central  hole  is  an  Haversian  canal,  and  the  rings  are  layers  of  bony  tissue 
arranged  concentrically  around  the  central  canal,  and  termed  lamellae.  More- 
over, on  closer  examination  it  will  be  found  that  between  these  lamellae,  and 
therefore  also  arranged  concentrically  around  the  central  canal,  are  a  number  of 
little  dark  spots,  the  lacimae,  and  that  these  lacunae  are  connected  with  each  other 
a,nd  with  the  central  Haversian  canal  by  a  number  of  fine  dark  lines,  which  radiate 
Uke  the  spokes  of  a  wheel  and  are  called  canaliculi.  Filling  in  the  irregular  intervals 
which  are  left  between  these  circular  systems  are  other  lamellae,  with  their  lacunae 
and  canaliculi  running  in  various  directions,  but  more  or  less  curved  (Fig.  73); 
they  are  termed  interstitial  lamellae.  Again,  other  lamellae,  found  on  the  surface 
f  the  bone,  are  arranged  parallel  to  its  circumference;  they  are  termed  circum- 


90 


OSTEOLOGY 


I 


ferential,  or  by  some  authors  primary  or  fundamental  lamellae,  to  distinguish  them 
from  those  laid  down  around  the  axes  of  the  Haversian  canals,  which  are  then 
termed  secondaiy  or  special  lamellae. 

The  Haversian  canals,  seen  in  a  transverse  section  of  bone  as  round  holes  at  or 
about  the  center  of  each  Haversian  system,  may  be  demonstrated  to  be  true  canah 
if  a  longitudinal  section  be  made  (Fig.  74).  It  will  then  be  seen  that  the  canals 
run  parallel  with  the  longitudinal  axis  of  the  bone  for  a  short  distance  and  then 
branch  and  communicate.  They  vary  considerably  in  size,  some  being  as  much  as 
0.12  mm.  in  diameter;  the  average  size  is,  however,  about  0.05  mm.  Near  the 
medullary  cavity  the  canals  are  larger  than  those  near  the  surface  of  the  bone. 
Each  canal  contains  one  or  two  bloodvessels,  with  a  small  quantity  of  delicate 
connective  tissue  and  some  nerve  filaments.  In  the  larger  ones  there  are  also 
lymphatic  vessels,  and  cells  with  branching  processes  which  communicate,  through 
the  canalculi,  with  the  branched  processes  of  certain  bone  cells  in  the  substance 
of  the  bone.  Those  canals  near  the  surface  of  the  bone  open  upon  it  by  minute 
orifices,  and  those  near  the  medullary  cavity  open  in  the  same  way  into  this  space, 
so  that  the  whole  of  the  bone  is  permeated  by  a  system  of  bloodvessels  running 
through  the  bony  canals  in  the  centers  of  the  Haversian  systems. 

The  lamellae  are  thin  plates  of  bony  tissue 
encircling  the  central  canal,  and  may  be  com- 
pared, for  the  sake  of  illustration,  to  a  number 
of  sheets  of  paper  pasted  one  over  another 
around  a  central  hollow  cylinder.  After 
macerating  a  piece  of  bone  in  dilute  mineral 
acid,  these  lamellae  may  be  stripped  off  in  a 


Fig.  74. — Settion  parallel  to  the  surface 
from  the  body  of  the  femur.  X  100.  o,  Haver- 
sian canals;  b,  lacunffi  seen  from  the  side;  c, 
others  seen  from  the  surface  in  lamellae,  which 
are  cut  horizontally. 


FiQ.  75. — Perforating  fibers,  human  parietal  bone,  decalcified. 
(H.  Muller.)  o,  perforating  fibers  in  situ;  b,  fibres  drawn  out  of 
their  sockets;  c,  sockets. 


longitudinal  direction  as  thin  films.  If  one  of  these  be  examined  with  a  high  power 
of  the  microscope,  it  will  be  found  to  be  composed  of  a  finely  reticular  structure, 
made  up  of  very  slender  transparent  fibers,  decussating  obliquely;  and  coalescing 
at  the  points  of  intersection ;  these  fibers  are  composed  of  fine  fibrils  identical  with 
those  of  white  connective  tissue.  The  intercellular  matrix  between  the  fibers  is 
impregnated  by  calcareous  deposit  which  the  acid  dissolves.  In  many  places  the 
various  lamellae  may  be  seen  to  be  held  together  by  tapering  fibers,  which  run 
obliquely  through  them,  pinning  or  bolting  them  together;  they  were  first  de- 
scribed by  Sharpey,  and  were  named  by  him  perforating  fibers  (Fig.  75). 

The  Lacunae  are  situated  between  the  lamellae,  and  consist  of  a  number  of  oblong 


I 


BONE 


91 


^ 


¥ 


ta 


spaces.  In  an  ordinary  microscopic  section,  viewed  by  transmitted  light,  tliey 
appear  as  fusiform  opaque  spots.  Each  lacuna  is  occupied  during  life  by  a  branched 
cell,  termed  a  bone-cell  or  bone-corpuscle,  the  processes  from  which  extend  into  the 
canaliculi  (Fig.  76). 

The  Canaliculi  are  exceedingly  minute  channels,  crossing  the  lamellae  and  con- 
necting the  lacunae  with  neighboring  lacunae  and  also  with  the  Haversian  canal. 
From  the  Haversian  canal  a  number  of  canaliculi  are  given  off,  which  radiate  from 
it,  and  open  into  the  first  set  of  lacunae  between  the  first  and  second  lamellae. 
From  these  lacunae  a  second  set  of  canaliculi  is  given  off;  these  run  outward  to  the 
next  series  of  lacunae,  and  so  on  until  the  periphery  of  the  Haversian  system  is 
reached;  here  the  canaliculi  given  off  from  the  last  series  of  lacunae  do  not  communi- 
cate with  the  lacunae  of  neighboring  Haversian  systems,  but  after  passing  outward 
for  a  short  distance  form  loops  and  return  to  their  own  lacunae.  Thus  every 
part  of  an  Haversian  system  is  supplied  with  nutrient  fluids  derived  from  the 
vessels  in  the  Haversian  canal  and  distributed 
through  the  canaliculi  and  lacunae. 

The  bone  cells  are  contained  in  the  lacunae, 
which,  however,  they  do  not  completely  fill. 
They  are  flattened  nucleated  branched  cells, 
homologous  with  those  of  connective  tissue;  the 
branches,  especially  in  young  bones,  pass  into 
the  canaliculi  from  the  lacunae. 

In  thin  plates  of  bone  (as  in  the  walls  of 
the  spaces  of  cancellous  tissue)  the  Haversian 
[  canals  are  absent,  and  the  canaliculi  open  into 
the  spaces  of  the  cancellous  tissue  (medullary 
spaces),  which  thus  have  the  same  function  as 
the  Haversian  canals. 

Chemical  Composition. — Bone  consists  of  an 
animal  and  an  earthy  part  intimately  com- 
bined together. 

I  The  animal  part  may  be  obtained  by  immersing  a  bone  for  a  considerable  time 
in  dilute  mineral  acid,  after  which  process  the  bone  comes  out  exactly  the  same 
shape  as  before,  but  perfectly  flexible,  so  that  a  long  bone  (one  of  the  ribs,  for 
example)  can  easily  be  tied  in  a  knot.  If  now  a  transverse  section  is  made 
(Fig.  77)  the  same  general  arrangement  of  the  Haversian  canals,  lamellae,  lacunae, 
and  canaliculi  is  seen. 

The  earthy  part  may  be  separately  obtained  by  calcination,  by  which  the 

animal  matter  is  completely  burnt  out.     The  bone  will  still  retain  its  original 

form,  but  it  will  be  white  and  brittle,  will  have  lost  about  one-third  of  its  original 

I  weight,  and  will  crumble  down  with  the  slightest  force.     The  earthy  matter  is 

I  composed  chiefly  of  calcium  phosphate,  about  58  per  cent,  of  the  weight  of  the 

I  bone,  calcium  carbonate  about  7  per  cent.,  calciimi  fluoride  and  magnesium  phos- 

"  phate  from  1  to  2  per  cent,  each  and  sodium  chloride  less  than  1  per  cent. ;  they  confer 

on  bone  its  hardness  and  rigidity,  while  the  animal  matter  (ossein)  determines  its 

I  tenacity. 
Ossification. — Some  bones  are  preceded  by  membrane,  such  as  those  forming 
the  roof  and  sides  of  the  skull;  others,  such  as  the  bones  of  the  limbs,  are  preceded 
by  rods  of  cartilage.     Hence  two  kinds  of  ossification  are  described:  the  intra- 
membranous  and  the  intracartilaginous. 

(Intramembranous  Ossification. — In  the  case  of  bones  which  are  developed 
in  membrane,  no  cartilaginous  mould  precedes  the  appearance  of  the  bony  tissue. 
The  membrane  which  occupies  the  place  of  the  future  bone  is  of  the  nature  of  con- 
nective tissue,  and  ultimately  forms  the  periosteum;  it  is  composed  of  fibers  and 
granular  cells  in  a  matrix.    The  peripheral  portion  is  more  fibrous,  while,  in  the 


Fig.  76. — Nucleated  bone  cells  and  their 
processes,  contained  in  the  bone  lacunae  and 
their  canaliculi  respectively.  From  a  section 
through  the  vertebra  of  an  adult  mouse. 
(Klein  and  Noble  Smith.) 


92 


OSTEOLOGY 


I 


interior  the  cells  or  osteoblasts  predominate;  the  whole  tissue  is  richly  supplied  with 
bloodvessels.  At  the  outset  of  the  process  of  bone  formation  a  little  network 
of  spicules  is  noticed  radiating  from  the  point  or  center  of  ossification.  These 
rays  consist  at  their  growing  points  of  a  network  of  fine  clear  fibers  and  granular 


Haversian  canal 


Bone  corpuscle 


Bone  corpuscle 
between  inter- 
stitial lamellee 


Fig.  77. — Transverse  section  of  body  of  human  fibula,  decalcified.      X  250. 

corpuscles  with  an  intervening  ground  substance  (Fig.  78).  The  fibers  are  termed 
osteogenetic  fibers,  and  are  made  up  of  fine  fibrils  differing  little  from  those  of  white 
fibrous  tissue.  The  membrane  soon  assumes  a  dark  and  granular  appearance  from 
the  deposition  of  calcareous  granules  in  the  fibers  and  in  the  intervening  matrix, 


Union  of 
adjacent  ~~' 
spicules 


Osteoblasts^^ 


Osteogenetic 
fibers 


Calcified  deposit 

between  the  fibers 


Bony  spicvlea 

FiQ.  78. — Part  of' the  growing  edge  of  the  developing  parietal  bone  of  a  fetal  cat.     (After  J.  Lawrence.) 

and  in  the  calcified  material  some  of  the  granular  corpuscles  or  osteoblasts  are 
enclosed.  By  the  fusion  of  the  calcareous  granules  the  tissue  again  assumes  a 
more  transparent  appearance,  but  the  fibers  are  no  longer  so  distinctly  seen. 
The  involved  osteoblasts  form  the  corpuscles  of  the  future  bone,  the  spaces  in 


I 


BONE 


93 


■ 


which  they  are  enclosed  constituting  the  lacunae.  As  the  osteogenetic  fibers  grow 
out  to  the  periphery  they  continue  to  calcify,  and  give  rise  to  fresh  bone  spicules. 
Thus  a  network  of  bone  is  formed,  the  meshes  of  which  contain  the  bloodvessels 
and  a  delicate  connective  tissue  crowded  with  osteoblasts.  The  bony  trabeculse 
thicken  by  the  addition  of  fresh  layers  of  bone  formed  by  the  osteoblasts  on  their 
surface,  and  the  meshes  are  correspondingly  encroached  upon.  Subsequently, 
successive  layers  of  bony  tissue  are  deposited  under  the  periosteum  and  around 
the  larger  vascular  channels  which  become  the  Haversian  canals,  so  that  the  bone 
increases  much  in  thickness. 

Intercartilaginous  Ossification. — Just  before  ossification  begins  the  mass  is 
entirely  cartilaginous,  and  in  a  long  bone,  which  may  be  taken  as  an  example,  the 
process  commences  in  the  center  and  proceeds  toward  the  extremities,  which  for 
some  time  remain  cartilaginous.  Subsequently  a  similar  process  commences  in 
one  or  more  places  in  those  extremities  and  gradually  extends  through  them. 
The  extremities  do  not,  however,  become  joined  to  the  body  of  the  bone  by  bony 
tissue  until  growth  has  ceased ;  between  the  body  and  either  extremity  a  layer  of 
cartilaginous  tissue  termed  the  epiphysial  cartilage  persists  for  a  definite  period; 

The  first  step  in  the  ossification  of 
the  cartilage  is  that  the  cartilage  cells, 
at  the  point  where  ossification  is  com- 
mencing and  which  is  termed  a  center 
of  ossification,  enlarge  and  arrange 
themselves  in  rows  (Fig.  79).  The 
matrix  in  which  they  are  imbedded 
increases  in  quantity,  so  that  the  cells 
become  further  separated  from  each 
other.  A  deposit  of  calcareous  material 
now  takes  place  in  this  matrix,  between 
the  rows  of  cells,  so  that  they  become 
separated  from  each  other  by  longi- 
tudinal columns  of  calcified  matrix, 
presenting  a  granular  and  opaque  ap- 
pearance. Here  and  there  the  matrix 
between  two  cells  of  the  same  row  also 
becomes  calcified,  and  transverse  bars 
of  calcified  substance  stretch  across 
from  one  calcareous  column  to  another. 
Thus  there  are  longitudinal  groups  of 
the  cartilage  cells  enclosed  in  oblong 
cavities,  the  walls  of  which  are  formed 
of  calcified  matrix  which  cuts  off  all 
nutrition  from  the  cells;  the  cells,  in 
consequence,  atrophy,  leaving  spaces 
called  the  primary  areolae. 

At  the  same  time  that  this  process 
is  going  on  in  the  center  of  the  solid 
bar  of    cartilage,   certain   changes   are 

I  taking  place  on  its  surface.     This  is 

I  covered  by  a  very  vascular  membrane, 

I  the  perichondrium,  entirely  similar  to  the 
embryonic  connective  tissue  already 
described  as  constituting  the  basis  of 
membrane  bone;  on  the  inner  surface  of  this — that  is  to  say,  on  the  surface  in 
contact  with  the  cartilage — are  gathered  the  formative  cells,  the  osteoblasts.  By 
the  agency  of  these  cells  a  thin  layer  of  bony  tissue  is  formed  between  the  peri- 


vnu 


Fig.  79. — Section  of  fetal  bone  of  cat.  tV.  Irruption 
of  the  subperiosteal  tissue,  p.  Fibrous  layer  of  the  pierios- 
teum.  o.  Layer  of  osteoblasts,  im.  Subperiosteal  bony 
deposit.     (From  Quain's  "Anatomy,"  E.  A.  Schafer.) 


OSTEOLOGY 


I 


chondrium  and  the  cartilage,  by  the  intramembranons  mode  of  ossification  just 
described.  There  are  then,  in  this  first  stage  of  ossification,  two  processes  going 
on  simultaneously:  in  the  center  of  the  cartilage  the  formation  of  a  number  of 
oblong  spaces,  formed  of  calcified  matrix  and  containing  the  withered  cartilage 
cells,  and  on  the  surface  of  the  cartilage  the  formation  of  a  layer  of  true  mem- 
brane bone.  The  second  stage  consists  in  the  prolongation  into  the  cartilage  of 
processes  of  the  deeper  or  osteogenetic  layer  of  the  perichondrium,  which  has 
now  become  periosteum  (Fig.  79,  ir).  The  processes  consist  of  bloodvessels  and 
cells — osteoblasts,  or  bone-formers,  and  osteoclasts,  or  bone-destroyers.  The  latter 
are  similar  to  the  giant  cells  (myeloplaxes)  found  in  marrow,  and  they  excavate 
passages  through  the  new-formed  bony  layer  by  absorption,  and  pass  through 
it  into  the  calcified  matrix  (Fig.  80).  Wherever  these  processes  come  in  con- 
tact with  the  calcified  walls  of  the  primary  areolae  they  absorb  them,  and  thus 
cause  a  fusion  of  the  original  cavities  and  the  formation  of  larger  spaces,  which 
are  termed  the  secondary  areolae  or  medullary  spaces.  These  secondary  spaces 
become  filled  with  embryonic  marrow,  consisting  of  osteoblasts  and  vessels,  derived, 

in  the  manner  described  above,  from  the 
osteogenetic  layer  of  the  periosteum  (Fig.  80) . 
Thus  far  there  has  been  traced  the  forma- 
tion of  enlarged  spaces  (secondary  areolae), 
the  perforated  walls  of  which  are  still  formed 
by  calcified  cartilage  matrix,  containing  an 
embryonic  marrow  derived  from  the  processes 
sent  in  from  the  osteogenetic  layer  of  the 
periosteum,  and  consisting  of  bloodvessels  and 
osteoblasts.  The  walls  of  these  secondary 
areolae  are  at  this  time  of  only  inconsiderable 
thickness,  but  they  become  thickened  by  the 
deposition  of  layers  of  true  bone  on  their  sur- 
face. This  process  takes  place  in  the  follow- 
ing manner:  Some  of  the  osteoblasts  of  the 
embryonic  marrow,  after  undergoing  rapid 
division,  arrange  themselves  as  an  epithelioid 
layer  on  the  surface  of  the  wall  of  the  space 
(Fig.  81).  This  layer  of  osteoblasts  forms  a 
bony  stratum,  and  thus  the  wall  of  the  space 
becomes  gradually  covered  with   a  layer  of 


Osteoclasts ^f''"^' 


Fig.  80. — Part  of  a  longitudinal  section  of 
the  developing  femur  of  a  rabbit,  a.  Flattened 
cartilage  cells,  h.  Enlarged  cartilage  cells,  c, 
d.  Newly  formed  bone.  e.  Osteoblasts.  /. 
Giant  cells  or  osteoclasts.  g,  h.  Shrunken 
cartilage  cells.  (From  "Atlas  of  Histology," 
Ivlein  and  Noble  Smith.) 


Osteoblasts 


ug^!,;^^.:3^^W 


Fig.  81. — Osteoblasts  and  osteoclasts  on  trabecula  of  lower  jaw  of 
calf  embryo.     (KoUiker.) 


true  osseous  substance  in  which  some  of  the  bone-forming  cells  are  included  as 
bone  corpuscles.  The  next  stage  in  the  process  consists  in  the  removal  of  these 
primary  bone  spicules  by  the  osteoclasts.  One  of  these  giant  cells  may  be  found 
lying  in  a  Howship's  foveola  at  the  free  end  of  each  spicule.    The  removal  of  the 


I 


BONE  ^^^^^^^K  95 


Pi 


primary  spicules  goes  on  pari  passu  with  the  formation  of  permanent  bone  by 
the  periosteum,  and  in  this  way  the  medullary  cavity  of  the  body  of  the  bone  is 
formed. 

This  series  of  changes  has  been  gradually  proceeding  toward  the  end  of  the  body 
of  the  bone,  so  that  in  the  ossifying  bone  all  the  changes  described  above  may 
be  seen  in  different  parts,  from  the  true  bone  at  the  center  of  the  body  to  the  hyaline 
cartilage  at  the  extremities. 

While  the  ossification  of  the  cartilaginous  body  is  extending  toward  the  articular 
ends,  the  cartilage  immediately  in  advance  of  the  osseous  tissue  continues  to  grow 
until  the  length  of  the  adult  bone  is  reached. 

During  the  period  of  growth  the  articular  end,  or  epiphysis,  remains  for  some 
time  entirely  cartilaginous,  then  a  bony  center  appears,  and  initiates  in  it  the 
process  of  intracartilaginous  ossification;  but  this  process  never  extends  to  any 
great  distance.     The  epiphysis  remains  separated  from  the  body  by  a  narrow 
cartilaginous  layer  for  a  definite  time.    This  layer  ultimately  ossifies,  the  distinc- 
tion between  body  and  epiphysis  is  obliterated,  and  the  bone  assumes  its  completed 
form  and  shape.    The  same  remarks  also  apply  to  such  processes  of  bone  as  are 
separately  ossified,  e.  g.,  the  trochanters  of  the  femur.    The  bones  therefore  con- 
tinue to  grow  until  the  body  has  acquired  its  full  stature.    They  increase  in  length 
by  ossification  continuing  to  extend  behind  the  epiphysial  cartilage,  w^hich  goes 
on  growing  in  advance  of  the  ossifying  process.    They  increase  in  circumference 
by  deposition  of  new  bone,  from  the  deeper  layer  of  the  periosteum,  on  their  exter- 
nal surface,  and  at  the  same  time  an  absorption  takes  place  from  within,  by  which 
I  the  medullary  cavities  are  increased. 
}    The  permanent  bone  formed  by  the  periosteum  when  first  laid  down  is  cancellous 
In  structure.    Later  the  osteoblasts  contained  in  its  spaces  become  arranged  in 
jthe  concentric  layers  characteristic  of  the  Haversian  systems,  and  are  included 
[as  bone  corpuscles. 
The  number  of  ossific  centers  varies  in  different  bones.    In  most  of  the  short 
bones  ossification  commences  at  a  single  point  near  the  center,  and  proceeds  toward 
^_  the  surface.    In  the  long  bones  there  is  a  central  point  of  ossification  for  the  body 
^|[or  diaphysis:  and  one  or  more  for  each  extremity,  the  epiphysis.    That  for  the 
^f  -body  is  the  first  to  appear.    The  times  of  union  of  the  epiphyses  with  the  body 
W    vary  inversely  with  the  dates  at  which  their  ossifications  began  (with  the  exception 
of  the  fibula)  and  regulate  the  direction  of  the  nutrient  arteries  of  the  bones.    Thus, 

I  the  nutrient  arteries  of  the  bones  of  the  arm  and  forearm  are  directed  toward 
rthe  elbow,  since  the  epiphyses  at  this  joint  become  united  to  the  bodies  before 
jthose  at  the  opposite  extremities.  In  the  low^er  limb,  on  the  other  hand,  the 
Inutrient  arteries  are  directed  away  from  the  knee:  that  is,  upward  in  the  femur, 
[downward  in  the  tibia  and  fibula;  and  in  them  it  is  observed  that  the  upper  epiphysis 
of  the  femur,  and  the  lower  epiphyses  of  the  tibia  and  fibula,  unite  first  with  the 
bodies.  Where  there  is  only  one  epiphysis,  the  nutrient  artery  is  directed  toward 
the  other  end  of  the  bone;  as  toward  the  acromial  end  of  the  clavicle,  toward  the 

P  distal  ends  of  the  metacarpal  bone  of  the  thumb  and  the  metatarsal  bone  of  the 
fereat  toe,  and  toward  the  proximal  ends  of  the  other  metacarpal  and  metatarsal 
bones. 

Parsons^  groups  epiphyses  under  three  headings,  viz.:  (1)  pressure  epiphyses, 
appearing  at  the  articular  ends  of  the  bones  and  transmitting  "the  weight  of  the 

r,  body  from  bone  to  bone;"   (2)  traction  epiphyses,  associated  with  the  insertion 
lof  muscles  and  "originally  sesamoid  structures  though  not  necessarily  sesamoid 
bones;"  and  (3)  atavistic  epiphyses,  representing  parts  of  the  skeleton,  which  at 
one  time  formed  separate  bones,  but  which  have  lost  their  function,  "  and  only 
appear  as  separate  ossifications  in  early  life." 
..,...,  ....„.,  P...,™,..  „„..„..... 


96 


OSTEOLOGY 


THE  VERTEBRAL  COLUMN  (COLUMNA  VERTEBRALIS ;  SPINAL 

COLUMN). 

The  vertebral  column  is  a  flexuous  and  flexible  column,  formed  of  a  series  o! 
bones  called  vertebrae. 

The  vertebrae  are  thirty-three  in  number,  and  are  grouped  under  the  names 
cervical,  thoracic,  lumbar,  sacral,  and  coccygeal,  according  to  the  regions  they 
occupy;  there  are  seven  in  the  cervical  region,  twelve  in  the  thoracic,  five  in  the 
lumbar,  five  in  the  sacral,  and  four  in  the  coccygeal. 

This  number  is  sometimes  increased  by  an  additional  vertebra  in  one  region, 
or  it  may  be  diminished  in  one  region,  the  deficiency  often  being  supplied  by  an 
additional  vertebra  in  another.  The  number  of  cervical  vertebrae  is,  however, 
very  rarely  increased  or  diminished. 

The  vertebrae  in  the  upper  three  regions  of  the  column  remain  distinct  through- 
out life,  and  are  known  as  true  or  movable  vertebrae;  those  of  the  sacral  and 
coccygeal  regions,  on  the  other  hand,  are  termed  false  or  fixed  vertebrae,  because 
they  are  united  with  one.  another  in  the  adult  to  form  two  bones — five  forming 
the  upper  bone  or  sacrum,  and  four  the  terminal  bone  or  coccyx. 

With  the  exception  of  the  first  and  second  cervical,  the  true  or  movable  vertebrae 
present  certain  common  characteristics  which  are  best  studied  by  examining  one 
from  the  middle  of  the  thoracic  region. 

GENERAL   CHARACTERISTICS    OF   A    VERTEBRA. 

A  typical  vertebra  consists  of  two  essential  parts — viz.,  an  anterior  segment,  the 
body,  and  a  posterior  part,  the  vertebral  or  neural  arch;  these  enclose  a  foramen, 
the  vertebral  foramen.  The  vertebral  arch  consists  of  a  pair  of  pedicles  and  a  pair 
of  laminae,  and  supports  seven  processes — viz.,  four  articular,  two  transverse,  and 
one  spinous. 


Costal  fovea 

Pedicle  or  roof  of 
vertebral  arch 


Lamina 


Superior  articular  process 


Fig.  82. — A  typical  thoracic  vertebra,  viewed  from  above. 


When  the  vertebrae  are  articulated  with  each  other  the  bodies  form  a  strong 
pillar  for  the  support  of  the  head  and  trunk,  and  the  vertebral  foramina  constitute 
a  canal  for  the  protection  of  the  medulla  spinalis  {spinal  cord),  while  between 
every  pair  of  vertebrae  are  two  apertures,  the  intervertebral  foramina,  one  on 
either  side,  for  the  transmission  of  the  spinal  nerves  and  vessels. 

Body  (corpus  vertebrce). — ^The  body  is  the  largest  part  of  a  vertebra,  and  is 
more  or  less  cylindrical  in  shape.    Its  upper  and  lower  surfaces  are  flattened  and 


THE  CERVICAL  VERTEBRA 


rough,  and  give  attachment  to  the  intervertebral  fibrocartilages,  and  each  presents 
a  rim  around  its  circumference.  In  front,  the  body  is  convex  from  side  to  side 
and  concave  from  above  downward.  Behind,  it  is  flat  from  above  downward 
and  slightly  concave  from  side  to  side.  Its  anterior  surface  presents  a  few  small 
apertures,  for  the  passage  of  nutrient  vessels;  on  the  posterior  surface  is  a  single 
large,  irregular  aperture,  or  occasionally  more  than  one,  for  the  exit  of  the  basi- 
vertebral veins  from  the  body  of  the  vertebra. 

Pedicles  {radices  arci  vertebroe). — The  pedicles  are  two  short,  thick  processes, 
which  project  backward,  one  on  either  side,  from  the  upper  part  of  the  body, 
at  the  junction  of  its  posterior  and  lateral  surfaces.  The  concavities  above  and 
below  the  pedicles  are  named  the  vertebral  notches;  and  when  the  vertebrae  are 
articulated,  the  notches  of  each  contiguous  pair  of  bones  form  the  intervertebral 
foramina,  already  referred  to. 

Laminae. — The  laminae  are  two  broad  plates  directed  backward  and  medialward 
from  the  pedicles.  They  fuse  in  the  middle  line  posteriorly,  and  so  complete  the 
posterior  boundary  of  the  vertebral  foramen.  Their  upper  borders  and  the  lower 
parts  of  their  anterior  surfaces  are  rough  for  the  attachment  of  the  ligamenta 
flava. 

Processes. — Spinous  Process  {processus  spinosus). — The  spinous  process  is 
directed  backward  and  downward  from  the  junction  of  the  laminae,  and  serves 
for  the  attachment  of  muscles  and  ligaments. 

Articular  Processes. — The  articular  processes,  two  superior  and  two  inferior, 
spring  from  the  junctions  of  the  pedicles  and  laminae.  The  superior  project 
upward,  and  their  articular  surfaces  are  directed  more  or  less  backward;  the 
inferior  project  downward,  and  their  surfaces  look  more  or  less  forward.  The 
articular  surfaces  are  coated  with  hyaline  cartilage. 

Transverse  Processes  {processus  transversi). — ^The  transverse  processes,  two  in 
number,  project  one  at  either  side  from  the  point  where  the  lamina  joins  the 
pedicle,  between  the  superior  and  inferior  articular  processes.  They  serve  for 
'the  attachment  of  muscles  and  ligaments. 

Stnictore  of  a  Vertebra  (Fig.  83). — The  body  is  composed  of  cancellous  tissue,  covered  by 

a  thin  coating  of  compact  bone;  the  latter  is  perforated  by  numerous  orifices,  some  of  large  size 
I  for  the  passage  of  vessels;  the  interior  of  the  bone  is  traversed  by  one  or  two  large  canals,  for  the 
[reception  of  veins,  which  converge  toward  a  single  large,  irregular  aperture,  or  several  small 

apertures,  at  the  posterior  part  of  the 

body.     The  thin  bony  lamellae  of  the 

cancellous  tissue  are  more  pronounced 

in  lines  perpendicular  to  the  upper 

and  low^er  surfaces  and  are  developed 

in  response  to  greater  pressure  in  this 

direction    (Fig.   83).     The  arch  and 

processes    projecting    from    it    have 

thick  coverings  of  compact  tissue. 

The  Cervical  Vertebrae  (Verte- 
brae Cervicales). 

The  cervical  vertebrae  (Fig. 
84)  are  the  smallest  of  the  true 
vertebrae,  and   can   be   readily 

distinguished  from  those  of  the  thoracic  or  lumbar  regions  by  the  presence  of  a 
foramen  in  each  transverse  process.  The  first,  second,  and  seventh  present  excep- 
tional features  and  must  be  separately  described ;  the  following  characteristics  are 
k common  to  the  remaining  four. 
The  body  is  small,  and  broader  from  side  to  side  than  from  before  backward 
The  anterior  and  posterior  surfaces  are  flattened  and  of  equal  depth;  the  former 


Fig.  83. — Sagittal  section  of  a  lumbar  vertebra. 


^ 


98 


OSTEOLOGY 


is  placed  on  a  lower  level  than  the  latter,  and  its  inferior  border  is  prolongeo 
downward,  so  as  to  overlap  the  upper  and  forepart  of  the  vertebra  below.  The 
upper  surface  is  concave  transversely,  and  presents  a  projecting  lip  on  either  side ; 
the  lower  surface  is  concave  from  before  backward,  convex  from  side  to  side,  and 
presents  laterally  shallow  concavities  which  receive  the  corresponding  projecting 
lips  of  the  subjacent  vertebra.  The  pedicles  are  directed  lateralward  and  l3ackward, 
and  are  attached  to  the  body  midway  between  its  upper  and  lower  borders,  so  that 
the  superior  vertebral  notch  is  as  deep  as  the  inferior,  but  it  is,  at  the  same  time. 


Anterior  tubercle  of 
transverse  'process 
Foramen 
iransversarium 
Posterior  tvbercle  of—^ 
transverse  process 


Transverse  process 


Superior  articular 
process 

Inferior  articular 
process 


I  Spinmis 
process 

Fig.  84. — A  cervical  vertebra. 


narrower.  The  laminse  are  narrow,  and  thinner  above  than  below;  the  vertebral 
foramen  is  large,  and  of  a  triangular  form.  The  spinous  process  is  short  and  bifid, 
the  two  divisions  being  often  of  unequal  size.  The  superior  and  inferior  articular 
processes  on  either  side  are  fused  to  form  an  articular  pillar,  which  projects  lateral- 
ward  from  the  junction  of  the  pedicle  and  lamina.  The  articular  facets  are  flat 
and  of  an  oval  form:  the  superior  look  backward,  upward,  and  slightly  medial- 
ward:  the  inferior  forward,  downward,  and  slightly  lateralward.  The  transverse 
processes  are  each  pierced  by  the  foramen  transversarium,  which,  in  the  upper  six 


Body 

Anterior  tubercle  of 
transverse  process 


Svlcusfor  nerve 


Superior  articular  surface 
Articular  pillar 


Fig.  85. 


Posterior  tubercle  of 
transverse  process 

■Side  view  of  a  typical  cervical  vertebra. 


Spinous  process 


vertebrae,  gives  passage  to  the  vertebral  artery  and  vein  and  a  plexus  of  sympa- 
thetic nerves.  Each  process  consists  of  an  anterior  and  a  posterior  part.  The 
anterior  portion  is  the  homologue  of  the  rib  in  the  thoracic  region,  and  is  there- 
fore named  the  costal  process  or  costal  element:  it  arises  from  the  side  of  the  body, 
is  directed  lateralward  in  front  of  the  foramen,  and  ends  in  a  tubercle,  the  anterior 
tubercle.  The  posterior  part,  the  true  transverse  process,  springs  from  the 
vertebral  arch  behind  the  foramen,  and  is  directed  forward  and  lateralward;  it 
ends  in  a  flattened  vertical    tubercle,    the  posterior  tubercle.     These   two  parts 


I 


THE  CERVICAL  VERTEBRA 


99 


are  joined,  outside  the  foramen,  by  a  bar  of  bone  which  exhibits  a  deep  sulcus 
on  its  upper  surface  for  the  passage  of  the  corresponding  spinal  nerve. ^ 

First  Cervical  Vertebra. — The  first  cervical  vertebra  (Fig.  86)  is  named  the 
atlas  because  it  supports  the  globe  of  the  head.  Its  chief  peculiarity  is  that  it  has 
no  body,  and  this  is  due  to  the  fact  that  the  body  of  the  atlas  has  fused  with  that 
of  the  next  vertebra.  Its  other  peculiarities  are  that  it  has  no  spinous  process, 
is  ring-like,  and  consists  of  an  anterior  and  a  posterior  arch  and  two  lateral  masses. 
The  anterior  arch  forms  about  one-fifth  of  the  ring:  its  anterior  surface  is  convex, 
and  presents  at  its  center  the  anterior  tubercle  for  the  attachment  of  the  Longus 
colli  muscles;  posteriorly  it  is  concave,  and  marked  by  a  smooth,  oval  or  circular 
facet  (fovea  dentis),  for  articulation  with  the  odontoid  process  (dejis)  of  the  axis. 
The  upper  and  lower  borders  respectively  give  attachment  to  the  anterior  atlanto- 
occipital  membrane  and  the  anterior  atlantoaxial  ligament;  the  former  connects 
it  with  the  occipital  bone  above,  and  the  latter  with  the  axis  below.  The  posterior 
arch  forms  about  two-fifths  of  the  circumference  of  the  ring :  it  ends  behind  in  the 
posterior  tubercle,  which  is  the  rudiment  of  a  spinous  process  and  gives  origin  to 
the  Recti  capitis  posteriores  minores.  The  diminutive  size  of  this  process  pre- 
vents any  interference  with  the  movements  between  the  atlas  and  the  skull. 
The  posterior  part  of  the  arch  presents  above  and  behind  a  rounded  edge  for 


Anterior  tvbercle 


Outline  of  section  of  odontoid 
process 
Outline  cf  section  of  trans- 
verse atlantal  ligament 


Foramen 
transver- 
sarium 


Groove  for  vertebral  artery 
and  first  cervical  nerve 


I 


Posterior  tiibercle 

Fig.  86. — First  cervical  vertebra,  or  atlas. 

the  attachment  of  the  posterior  atlantooccipital  membrane,  while  immediately 
behind  each  superior  articular  process  is  a   groove   (sulcus   arteriw  wrtchralis), 

(sometimes  converted  into  a  foramen  by  a  delicate  bony  spiculum  which  arches 
backward  from  the  posterior  end  of  the  superior  articular  process.  This  groove 
represents  the  superior  vertebral  notch,  and  serves  for  the  transmission  of  the 
vertebral  artery,  which,  after  ascending  through  the  foramen  in  the  transverse 
process,  winds  around  the  lateral  mass  in  a  direction  backward  and  medialward;  it 
also  transmits  the  suboccipital  (first  spinal)  nerve.  On  the  under  surface  of  the 
posterior  arch,  behind  the  articular  facets,  are  two  shallow  grooves,  the  inferior 
vertebral  notches.  The  lower  border  gives  attachment  to  the  posterior  atlanto- 
axial ligament,  which  connects  it  with  the  axis.  The  lateral  masses  are  the  most 
bulky  and  solid  parts  of  the  atlas,  in  order  to  support  the  weight  of  the  head. 

(Each  carries  two  articular  facets,  a  superior  and  an  inferior.  The  superior  facets 
are  of  large  size,  oval,  concave,  and  approach  each  other  in  front,  but  diverge 
behind:  they  are  directed  upward,  medialward,  and  a  little  backward,  each  forming 
a  cup  for  the  corresponding  condyle  of  the  occipital  bone,  and  are  admirably 
adapted  to  the  nodding  movements  of  the  head.     Not  infrequently  they  are 

'  The  costal  element  of  a  cervical  vertebra  not  only  includes  the  portion  which  spriags  from  the  side  of  tlje  body,  but 
^the  anterior  and  posterior  tubercles  and  the  bar  of  bone  which  connects  them  (rig.  67). 


100 


OSTEOLOGY 


partially  subdivided  by  indentations  which  encroach  upon  their  margins.  The 
inferior  articular  facets  are  circular  in  form,  flattened  or  slightly  convex  and  directed 
downward  and  medialward,  articulating  with  the  axis,  and  permitting  the  rotatory 
movements  of  the  head.  Just  below  the  medial  margin  of  each  superior  facet  is 
a  small  tubercle,  for  the  attachment  of  the  transverse  atlantal  ligament  which 
stretches  across  the  ring  of  the  atlas  and  divides  the  vertebral  foramen  into  two 
unequal  parts — the  anterior  or  smaller  receiving  the  odontoid  process  of  the  axis, 
the  posterior  transmitting  the  medulla  spinalis  and  its  membranes.  This  part 
of  the  vertebral  canal  is  of  considerable  size,  much  greater  than  is  required  for  the 
accommodation  of  the  medulla  spinalis,  and  hence  lateral  displacement  of  the 
atlas  may  occur  without  compression  of  this  structure.  The  transverse  processes 
are  large;  they  project  lateralward  and  downward  from  the  lateral  masses,  and 
serve  for  the  attachment  of  muscles  which  assist  in  rotating  the  head.  They 
are  long,  and  their  anterior  and  posterior  tubercles  are  fused  into  one  mass;  the 
foramen  transversarium  is  directed  from  below,  upward  and  backward. 


Dens 


For  alar  ligaments 

For  trans,  ligament  of  atlas 

Superior  artiadar 
surface 


Foramen 

transversarium 


Spinous  process 
Fia.  87. — Second  cervical  vertebra,  or  epistropheus,  from  above. 


Second  Cervical  Vertebra. — ^The  second  cervical  vertebra  (Fig.  87  and  88)  is  named 
the  epistropheus  or  axis  because  it  forms  the  pivot  upon  which  the  first  vertebra, 
carrying  the  head,  rotates.  The  most  distinctive  characteristic  of  this  bone  is 
the  strong  odontoid  process  which  rises  perpendicularly  from  the  upper  surface 
of  the  body.  The  body  is  deeper  in  front  than  behind,  and  prolonged  downward 
anteriorly  so  as  to  overlap  the  upper  and  fore  part  of  the  third  vertebra.  It  pre- 
sents in  front  a  median  longitudinal  ridge,  separating  two  lateral  depressions  for 
the  attachment  of  the  Longus  colli  muscles.  Its  under  surface  is  concave  from 
before  backward  and  covex  from  side  to  side.  The  dens  or  odontoid  process  exhibits 
a  slight  constriction  or  neck,  where  it  joins  the  body.  On  its  anterior  surface 
is  an  oval  or  nearly  circular  facet  for  articulation  with  that  on  the  anterior  arch 
of  the  atlas.  On  the  back  of  the  neck,  and  frequently  extending  on  to  its  lateral 
surfaces,  is  a  shallow  groove  for  the  transverse  atlantal  ligament  which  retains 
the  process  in  position.  The  apex  is  pointed,  and  giAes  attacliment  to  the  apical 
odontoid  ligament;  below  the  apex  the  process  is  somewhat  enlarged,  and  pre- 
sents on  either  side  a  rough  impression  for  the  attachment  of  the  alar  ligament; 
these  ligaments  connect  the  process  to  the  occipital  bone.    The  internal  structure 


I 


THE  CERVICAL  VERTEBRA 


101 


of  the  odontoid  process  is  more  compact  than  that  of  the  body.  The  pedicles 
are  broad  and  strong,  espe;cially  in  front,  where  they  coalesce  with  the  sides  of 
the  body  and  the  root  of  the  odontoid  process.  They  are  covered  above  by  the 
superior  articular  surfaces.      The  laminae  are  thick  and  strong,  and  the  vertebral 


Odontoid  process 


Rough  surface  for  alar  ligament 
Groove  for  transverse  atlantal  ligament 


Spinous  process"^ 


Articular  facet  for 
anterior  arch  of 


Body 


Post,  root 


I 


Transverse  process 
Inferior  articular  process 

Fig.  88. — Second  cervical  vertebra,  epistropheus,  or  axis,  from  the  side. 


foramen  large,  but  smaller  than  that  of  the  atlas.  The  transverse  processes  are 
very  small,  and  each  ends  in  a  single  tubercle;  each  is  perforated  by  the  foramen 
transversarium,  which  is  directed  obliquely  upward  and  lateralward.  The  superior 
articular  surfaces  are  round,  slightly  convex,  directed  upward  and  lateralward, 
and  are   supported   on  the  body, 

pedicles,  and  transverse  processes.  ^'^^^ 

[The  inferior  articular  surfaces  have 
the  same  direction  as  those  of  the 
other  cervical  vertebrae.  The  supe- 
rior vertebral  notches  are  very  shal- 
low, and  lie  behind  the  articular 
k)rocesses;  the  inferior  lie  in  front 
of  the  articular  processes,  as  in  the 
other  cervical  vertebrae.  The  spinous 
process  is  large,  very  strong,  deeply 
channelled  on  its  under  surface, 
and  presents  a  bifid,  tuberculated 
extremity. 

The  Seventh  Cervical  Vertebra 
(Fig.  89). — The  most  distinctive 
characteristic  of  this  vertebra  is 
the  existence  of  a  long  and  promi- 
nent spinous  process,  hence  the 
name  vertebra  prominens.  This  pro- 
cess is  thick,  nearly  horizontal  in 
direction,  not  bifurcated,  but  ter- 
minating in  a  tubercle  to  which  the  lower  end  of  the  ligamentum  nuchse  is 
attached.  The  transverse  processes  are  of  considerable  size,  their  posterior  roots 
are  large  and  prominent,  while  the  anterior  are  small  and  faintly  marked;  the 
upper  surface  of  each  has  usually  a  shallow  sulcus  for  the  eighth  spinal  nerve, 
and  its  extremity  seldom  presents  more  than  a  trace  of  bifurcation.    The  foramen 


Spinous  process 
Fig.  89. — Seventh  cervical  vertebra. 


102 


OSTEOLOGY 


I 


transversarium  may  be  as  large  as  that  in  the  other  cervical  vertebrae,  but  is 
generally  smaller  on  one  or  both  sides;  occasionally  it  is  double,  sometimes  it  is 
absent.  On  the  left  side  it  occasionally  gives  passage  to  the  vertebral  artery; 
more  frequently  the  vertebral  vein  traverses  it  on  both  sides;  but  the  usual 
arrangement  is  for  both  artery  and  vein  to  pass  in  front  of  the  transverse  pro- 
cess, and  not  through  the  foramen.  Sometimes  the  anterior  root  of  the  trans- 
verse process  attains  a  large  size  and  exists  as  a  separate  bone,  which  is  known 
as  a  cervical  rib. 

The  Thoracic  Vertebrae  (Vertebrae  Thoracales). 

The  thoracic  vertebrae  (Fig.  90)  are  intermediate  in  size  between  those  of 
the  cervical  and  lumbar  regions;  they  increase  in  size  from  above  downward,  the 
upper  vertebrae  being  much  smaller  than  those  in  the  lower  part  of  the  region. 
They  are  distinguished  by  the  presence  of  facets  on  the  sides  of  the  bodies  for 
articulation  with  the  heads  of  the  ribs,  and  facets  on  the  transverse  processes  of 
all,  except  the  eleventh  and  twelfth,  for  articulation  with  the  tubercles  of  the  ribs. 


Superior  articular  process 


Demi-facet  for  head  of  rib 


Facet  for  articular  part 
of  tubercle  of  rib 


Demi-facet  for  head  of  rib 
Inferior  articular  process 


Fig.  90. — A  thoracic  vertebra. 


The  bodies  in  the  middle  of  the  thoracic  region  are  heart-shaped,  and  as  broad 
in  the  antero-posterior  as  in  the  transverse  direction.  At  the  ends  of  the  thoracic 
region  they  resemble  respectively  those  of  the  cervical  and  lumbar  vertebrae. 
They  are  slightly  thicker  behind  than  in  front,  flat  above  and  below,  convex  from 
side  to  side  in  front,  deeply  concave  behind,  and  slightly  constricted  laterally 
and  in  front.  They  present,  on  either  side,  two  costal  demi-facets,  one  above, 
near  the  root  of  the  pedicle,  the  other  below,  in  front  of  the  inferior  vertebral 
notch;  these  are  covered  with  cartilage  in  the  fresh  state,  and,  when  the  vertebrae 
are  articulated  with  one  another,  form,  with  the  intervening  intervertebral  fibro- 
cartilages,  oval  surfaces  for  the  reception  of  the  heads  of  the  ribs.  The  pedicles 
are  directed  backward  and  slightly  upward,  and  the  inferior  vertebral  notches 
are  of  large  size,  and  deeper  than  in  any  other  region  of  the  vertebral  column. 
The  laminae  are  broad,  thick,  and  imbricated — that  is  to  say,  they  overlap  those 
of  subjacent  vertebrae  like  tiles  on  a  roof.  The  vertebral  foramen  is  small,  and  of 
a  circular  form.  The  spinous  process  is  long,  triangular  on  coronal  section,  directed 
obliquely  downward,  and  ends  in  a  tuberculated  extremity.     These  processes 


I 


THE  THORACIC  VERTEBRAE 


103 


overlap  from  the  fifth  to  the  eighth,  but  are  less  oblique  in  direction  above  and 
below.  The  superior  articular  processes  are  thin  plates  of  bone  projecting  upward 
from  the  junctions  of  the  pedicles  and  laminse;  their  articular  facets  are  practi- 
cally flat,  and  are  directed  backward  and  a  little  lateralward  and  upward.  The 
inferior  articular  processes  are  fused  to  a  considerable  extent  with    the  laminse. 


An  entire  facet  above; 
a  demi-facet  below 


A  demi-facet  above 


—  One  entire  facet 


One  entire  facet. 
No  facet  on  trans,  proc. 
which  is  rudimentary 


One  entire  facet. 

(No  facet  on  trans- 
I      verse  process, 
-[  Infer.artic.process 
I  convex  and  turned 
\lateralivard3 


Fio.  91. — Peculiar  thoracic  vertebrse. 


I 


and  project  but  slightly  beyond  their  lower  borders;  their  facets  are  directed 
forward  and  a  little  medialward  and  downward.  The  transverse  processes  arise 
from  the  arch  behind  the  superior  articular  processes  and  pedicles;  they  are  thick, 
strong,  and  of  considerable  length,  directed  obliquely  backward  and  lateralward, 
and  each  ends  in  a  clubbed  extremity,  on  the  front  of  which  is  a  small,  concave 
surface,  for  articulation  with  the  tubercle  of  a  rib. 


104 


OSTEOLOGY 


The  first,  ninth,  tenth,  eleventh,  and  twelfth  thoracic  vertebrae  present  certaiai 
pecuHarities,  and  must  be  specially  considered  (Fig.  91). 

The  First  Thoracic  Vertebra  has,  on  either  side  of  the  body,  an  entire  articular 
facet  for  the  head  of  the  first  rib,  and  a  demi-facet  for  the  upper  half  of  the  head 
of  the  second  rib.  The  body  is  like  that  of  a  cervical  vertebra,  being  broad  trans- 
versely; its  upper  surface  is  concave,  and  lipped  on  either  side.  The  superior 
articular  surfaces  are  directed  upward  and  backward;  the  spinous  process  is  thick, 
long,  and  almost  horizontal.  The  transverse  processes  are  long,  and  the  upper 
vertebral  notches  are  deeper  than  those  of  the  other  thoracic  vertebrae. 

The  Ninth  Thoracic  Vertebra  may  have  no  demi-facets  below.  In  some  sub- 
jects however,  it  has  two  demi-facets  on  either  side;  when  this  occurs  the  tenth 
has  only  demi-facets  at  the  upper  part. 

The  Tenth  Thoracic  Vertebra  has  (except  in  the  cases  just  mentioned)  an  entire 
articular  facet  on  either  side,  which  is  placed  partly  on  the  lateral  surface  of  the 
pedicle. 

In  the  Eleventh  Thoracic  Vertebra  the  body  approaches  in  its  form  and  size 
to  that  of  the  lumbar  vertebrae.  The  articular  facets  for  the  heads  of  the  ribs 
are  of  large  size,  and  placed  chiefly  on  the  pedicles,  which  are  thicker  and  stronger 
in  this  and  the  next  vertebra  than  in  any  other  part  of  the  thoracic  region.  The 
spinous  process  is  short,  and  nearly  horizontal  in  direction.  The  transverse  processes 
are  very  short,  tuberculated  at  their  extremities,  and  have  no  articular  facets. 

The  Twelfth  Thoracic  Vertebra  has  the  same  general  characteristics  as  the- 
eleventh,  but  may  be  distinguished  from  it  by  its  inferior  articular  surfaces  being 
convex  and  directed  lateralward,  like  those  of  the  lumbar  vertebrae;  by  the  general 
form  of  the  body,  laminae,  and  spinous  process,  in  which  it  resembles  the  lumbar 
vertebrae;  and  by  each  transverse  process  being  subdivided  into  three  elevations, 
the  superior,  inferior,  and  lateral  tubercles:  the  superior  and  inferior  correspond 
to  the  mammillary  and  accessory  processes  of  the  lumbar  vertebrae.  Traces  of 
similar  elevations  are  found  on  the  transverse  processes  of  the  tenth  and  eleventh 
thoracic  vertebrae. 


Superior  articular  process 


Fig.  92. — A  lumbar  vertebra  seen  from  the  side. 


The  Lumbar  Vertebrae  (Vertebrae  Lumbales). 

The  lumbar  vertebrae  (Figs.  92  and  93)  are  the  largest  segments  of  the  movable 
part  of  the  vertebral  column,  and  can  be  distinguished  by  the  absence  of  a 
foramen  in  the  transverse  process,  and  by  the  absence  of  facets  on  the  sides  of 
the  body. 

The  body  is  large,  wider  from  side  to  side  than  from  before  backward,  and  a 
little  thicker  in  front  than  behind.    It  is  flattened  or  slightly  concave  above  and 


I 


THE  LUMBAR  VERTEBRA 


105 


below,  concave  behind,  and  deeply  constricted  in  front  and  at  the  sides.     The 
pedicles  are  very  strong,  directed  backward  from  the  upper  part  of  the  body; 


Transverse  process 


Inferior  articular 
process 


Superior  articular 
process 


Mamillary  process 
Accessory  process 


FiQ.  93. — A  lumbar  vertebra  from  above  and  behind. 


consequently,  the  inferior  vertebral  notches  are  of  considerable  depth.     The 
laminse  are  broad,  short,  and  strong;  the  vertebral  foramen  is  triangular,  larger 


Fio.  94. — Fifth  lumbar  vertebra,  from  above. 


than  in  the  thoracic,  but  smaller  than  in  the  cervical  region.    The  spinous  process 
is  thick,  broad,  and  somewhat  quadrilateral;  it  projects  backward  and  ends  in 


I 


106  OSTEOLOGY 

a  rough,  uneven  border,  thickest  below  where  it  is  occasionally  notched.  Tht5^ 
superior  and  inferior  articular  processes  are  well-defined,  projecting  respectively 
upward  and  downward  from  the  junctions  of  pedicles  and  laminae.  The  facets 
on  the  superior  processes  are  concave,  and  look  backward  and  medial  ward;  thos(3 
on  the  inferior  are  convex,  and  are  directed  forward  and  lateral  ward.  The  former 
are  wider  apart  than  the  latter,  since  in  the  articulated  column  the  inferior  articular 
processes  are  embraced  by  the  superior  processes  of  the  subjacent  vertebra.  The 
transverse  processes  are  long,  slender,  and  .horizontal  in  the  upper  three  lumbar 
vertebrae;  they  incline  a  little  upward  in  the  lower  two.  In  the  upper  three  verte- 
brae they  arise  from  the  junctions  of  the  pedicles  and  laminae,  but  in  the  lower 
two  they  are  set  farther  forward  and  spring  from  the  pedicles  and  posterior  parts 
of  the  bodies.  They  are  situated  in  front  of  the  articular  processes  instead  of  behind 
them  as  in  the  thoracic  vertebrae,  and  are  homologous  with  the  ribs.  Of  the  three 
tubercles  noticed  in  connection  with  the  transverse  processes  of  the  lower  thoracic 
vertebrae,  the  superior  one  is  connected  in  the  lumbar  region  with  the  back  part 
of  the  superior  articular  process,  and  is  named  the  mammillary  process;  the  inferior 
is  situated  at  the  back  part  of  the  base  of  the  transverse  process,  and  is  called  the 
accessory  process  (Fig.  93). 

The  Fifth  Lumbar  Vertebra  (Fig.  94)  is  characterized  by  its  body  being  much 
deeper  in  front  than  behind,  which  accords  with  the  prominence  of  the  sacro- 
vertebral  articulation;  by  the  smaller  size  of  its  spinous  process;  by  the  wide  interval 
between  the  inferior  articular  processes;  and  by  the  thickness  of  its  transverse 
processes,  which  spring  from  the  body  as  well  as  from  the  pedicles. 

The  Sacral  and  Coccygeal  Vertebrae. 

The  sacral  and  coccygeal  vertebrae  consist  at  an  early  period  of  life  of  nine 
separate  segments  which  are  united  in  the  adult,  so  as  to  form  two  bones,  five 
entering  into  the  formation  of  the  sacrum,  four  into  that  of  the  coccyx.  Some- 
times the  coccyx  consists  of  five  bones;  occasionally  the  number  is  reduced  to 
three. 

The  Sacrum  {os  sacrum). — The  sacrum  is  a  large,  triangular  bone,  situated 
in  the  lower  part  of  the  vertebral  column  and  at  the  upper  and  back  part  of  the 
pelvic  cavity,  where  it  is  inserted  like  a  wedge  between  the  two  hip  bones;  its 
upper  part  or  base  articulates  with  the  last  lumbar  vertebra,  its  apex  with  the 
coccyx.  It  is  curved  upon  itself  and  placed  very  obliquely,  its  base  projecting 
forward  and  forming  the  prominent  sacrovertebral  angle  when  articulated  with 
the  last  lumbar  vertebra;  its  central  part  is  projected  backward,  so  as  to  give 
increased  capacity  to  the  pelvic  cavity. 

Pelvic  Surface  {jades  pelvina). — The  pelvic  surface  (Fig.  95)  is  concave  from 
above  downward,  and  slightly  so  from  side  to  side.  Its  middle  part  is  crossed 
by  four  transverse  ridges,  the  positions  of  which  correspond  with  the  original 
planes  of  separation  between  the  five  segments  of  the  bone.  The  portions  of  bone 
intervening  between  the  ridges  are  the  bodies  of  the  sacral  vertebrae.  The  body 
of  the  first  segment  is  of  large  size,  and  in  form  resembles  that  of  a  lumbar  vertebra; 
the  succeeding  ones  diminish  from  above  downward,  are  flattened  from  before 
backward,  and  curved  so  as  to  accommodate  themselves  to  the  form  of  the  sacrum, 
being  concave  in  front,  convex  behind.  At  the  ends  of  the  ridges  are  seen  the 
anterior  sacral  foramina,  four  in  number  on  either  side,  somewhat  rounded  in  form, 
diminishing  in  size  from  above  downward,  and  directed  lateralward  and  forward; 
they  give  exit  to  the  anterior  divisions  of  the  sacral  nerves  and  entrance  to  the 
lateral  sacral  arteries.  Lateral  to  these  foramina  are  the  lateral  parts  of  the  sacrum, 
each  consisting  of  five  separate  segments  at  an  early  period  of  life;  in  the  adult, 
these  are  blended  wdth  the  bodies  and  with  each  other.    Each  lateral  part  is  tra- 


I 


THE  SACRAL  AND  COCCYGEAL  VERTEBRAE 


107 


versed  by  four  broad,  shallow  grooves,  which  lodge  the  anterior  divisions  of  the 
sacral  nerves,  and  are  separated  by  prominent  ridges  of  bone  which  give  origin 
to  the  Piriformis  muscle. 

If  a  sagittal  section  be  made  through  the  center  of  the  sacrum  (Fig.  99),  the 
bodies  are  seen  to  be  united  at  their  circumferences  by  bone,  wide  intervals  being 
left  centrally,  which,  in  the  fresh  state,  are  filled  by  the  intervertebral  fibro- 
cartilages.  In  some  bones  this  union  is  more  complete  between  the  lower  than 
the  upper  segments. 

Dorsal  Surface  (fades  dorsalis). — The  dorsal  surface  (Fig.  96)  is  convex  and 
narrower  than  the  pelvic.  In  the  middle  line  it  displays  a  crest,  the  middle  sacral 
crest,  surmounted  by  three  or  four  tubercles,  the  rudimentary  spinous  processes 


Promontory 


FiQ.  95. — ^Sacrum,  pelvic  surface. 

rof  the  upper  three  or  four  sacral  vertebrae.  On  either  side  of  the  middle  sacral 
'crest  is  a  shallow  groove,  the  sacral  groove,  which  gives  origin  to  the  Multifidus, 
the  floor  of  the  groove  being  formed  by  the  united  laminae  of  the  corresponding 
vertebrs.  The  laminae  of  the  fifth  sacral  vertebra,  and  sometimes  those  of  the 
fourth,  fail  to  meet  behind,  and  thus  a  hiatus  or  deficiency  occurs  in  the  posterior 
wall  of  the  sacral  canal.  On  the  lateral  aspect  of  the  sacral  groove  is  a  linear 
series  of  tubercles  produced  by  the  fusion  of  the  articular  processes  which  together 
form  the  indistinct  sacral  articular  crests.  The  articular  processes  of  the  first 
sacral  vertebra  are  large  and  oval  in  shape;  their  facets  are  concave  from  side  to 
side,  look  backward  and  medialward,  and  articulate  with  the  facets  on  the  inferior 
processes  of  the  fifth  lumbar  \ertebra.  The  tubercles  which  represent  the  inferior 
articular  processes  of  the  fifth  sacral  vertebra  are  prolonged  downward  as  rounded 


108 


OSTEOLOGY 


I 


processes,  which  are  named  the  sacral  comua,  and  are  connected  to  the  corni:a 
of  the  coccyx.  Lateral  to  the  articular  processes  are  the  four  posterior  sacral 
foramina;  they  are  smaller  in  size  and  less  regular  in  form  than  the  anterior,  and 
transmit  the  posterior  divisions  of  the  sacral  nerves.  On  the  lateral  side  of  the 
posterior  sacral  foramina  is  a  series  of  tubercles,  which  represent  the  transverse 
processes  of  the  sacral  vertebrse,  and  form  the  lateral  crests  of  the  sacrum.  The 
transverse  tubercles  of  the  first  sacral  vertebra  are  large  and  very  distinct;  they, 
together  with  the  transverse  tubercles  of  the  second  vertebra,  give  attachment 
to  the  horizontal  parts  of  the  posterior  sacroiliac  ligaments;  those  of  the  third 
vertebra  give  attachment  to  the  oblique  fasciculi  of  the  posterior  sacroiliac  liga- 
ments; and  those  of  the  fourth  and  fifth  to  the  sacrotuberous  ligaments. 


Saerospinalis 


Latissimus 
dor  si 


Saerospinalis 


er  half  of  fifth 
posterior  sacral  foramen 


Fig.   96. — Sacrum,  dorsal  surface. 


Lateral  Surface. — The  lateral  surface  is  broad  above,  but  narrowed  into  a  thin 
edge  below.  The  upper  half  presents  in  front  an  ear-shaped  surface,  the  auricular 
surface,  covered  with  cartilage  in  the  fresh  state,  for  articulation  with  the  ilium. 
Behind  it  is  a  rough  surface,  the  sacral  tuberosity,  on  which  are  three  deep 
and  uneven  impressions,  for  the  attachment  of  the  posterior  sacroiliac  ligament. 
The  lower  half  is  thin,  and  ends  in  a  projection  called  the  inferior  lateral  angle; 
medial  to  this  angle  is  a  notch,  which  is  converted  into  a  foramen  by  the  trans- 
verse process  of  the  first  piece  of  the  coccyx,  and  transmits  the  anterior  division  of 
the  fifth  sacral  nerve.  The  thin  lower  half  of  the  lateral  surface  gives  attachment 
to  the  sacrotuberous  and  sacrospinous  ligaments,  to  some  fibers  of  the  Glutseus 
maximus  behind,  and  to  the  Coccygeus  in  front. 

Base  {basis  oss.  sacri). — The  base  of  the  sacrum,  which  is  broad  and  expanded, 
is  directed  upward  and  forward.    In  the  middle  is  a  large  oval  articular  surface, 


I 


THE  SACRAL  AND  COCCYGEAL  VERTEBRA 


109 


the  upper  surface  of  the  body  of  the  first  sacral  vertebra,  which  is  connected  with 
the  under  surface  of  the  body  of  the  last  lumbar  vertebra  by  an  intervertebral 


Articular  process 
Medial  sacral  crest 


Cornu  of  sacrum/ 

Cornu  of  coccyx 


Fig.  97. — Lateral  surfaces  of  sacrum  and  coccyx. 


Sacral  canal 

Articular  procesa 


Fig   98.— Base  of  sacrum. 


110 


OSTEOLOGY 


I 


fibrocartilage.  Behind  this  is  the  large  triangular  orifice  of  the  sacral  canal,  whicb 
is  completed  by  the  laminae  and  spinous  process  of  the  first  sacral  vertebra.  The 
superior  articular  processes  project  from  it  on  either  side;  they  are  oval,  concave;, 
directed  backward  and  medialward,  like  the  superior  articular  processes  of  a  lumbar 
vertebra.  They  are  attached  to  the  body  of  the  first  sacral  vertebra  and  to  the 
alae  by  short  thick  pedicles;  on  the  upper  surface  of  each  pedicle  is  a  vertebral 
notch,  which  forms  the  lower  part  of  the  foramen  between  the  last  lumbar  and  first 
sacral  vertebrae.  On  either  side  of  the  body  is  a  large  triangular  surface,  which 
supports  the  Psoas  major  and  the  lumbosacral  trunk,  and  in  the  articulated 
pelvis  is  continuous  with  the  iliac  fossa.    This  is  called  the  ala;  it  is  slightly  concave 


Cornua 


Anterior  Surface 


Posterior  surface 


Fia.  99. — Mediaa  sagittal  section  of  the  sacrum. 


Fig.  100.- 


from  side  to  side,  convex  from  before  backward,  and  gives  attachment  to  a  few 
of  the  fibers  of  the  Iliacus.  The  posterior  fourth  of  the  ala  represents  the  trans- 
verse process,  and  its  anterior  three-fourths  the  costal  process  of  the  first  sacral 
segment. 

Apex  {a'pex  oss.  sacri). — ^The  apex  is  directed  downward,  and  presents  an  oval 
facet  for  articulation  with  the  coccyx. 

Vertebral  Canal  (canalis  sacralis;  sacral  canal). — The  vertebral  canal  (Fig.  99) 
runs  throughout  the  greater  part  of  the  bone;  above,  it  is  triangular  in  form; 
below,  its  posterior  wall  is  incomplete,  from  the  non-development  of  the  laminae 
and  spinous  processes.  It  lodges  the  sacral  nerves,  and  its  walls  are  perforated  by 
the  anterior  and  posterior  sacral  foramina  through  which  these  nerves  pass  out. 


THE  SACRAL  AND  COCCYGEAL  VERTEBRA  111 


^^m-   Structure. — The  sacrum  consists  of  cancellous  tissue  enveloped  by  a  thin  layer  of  compact  bone. 

Articulations. — The  sacrum  articulates  with  four  bones;  the  last  lumbar  vertebra  above,  the 
coccyx  below,  and  the  hip  bone  on  either  side. 

Differences  in  the  Sacrum  of  the  Male  and  Female. — In  the  female  the  sacrum  is  shorter  and 
wider  than  in  the  male;  the  lower  half  forms  a  greater  angle  with  the  upper;  the  upper  half  is 
nearly  straight,  the  lower  half  presenting  the  greatest  amount  of  curvature.  The  bone  is  also 
directed  more  obliquely  backward;  this  increases  the  size  of  the  pelvic  cavity  and  renders  the 
sacrovertebral  angle  more  prominent.  In  the  male  the  curvature  is  more  evenly  distributed 
over  the  whole  length  of  the  bone,  and  is  altogether  greater  than  in  the  female. 

Variations. — The  sacrum,  in  some  cases,  consists  of  six  pieces;  occasionally  the  number  is 
reduced  to  four.  The  bodies  of  the  first  and  second  vertebra  may  fail  to  unite.  Sometimes 
the  uppermost  transverse  tubercles  are  not  joined  to  the  rest  of  the  ala  on  one  or  both  sides, 
or  the  sacral  canal  may  be  open  throughout  a  considerable  part  of  its  length,  in  consequence  of 
the  imperfect  development  of  the  laminse  and  spinous  processes.  The  sacrum,  also,  varies  con- 
siderably with  respect  to  its  degree  of  curvature. 

The  Coccyx  (os  coccygis). — The  coccyx  (Fig.  100)  is  usually  formed  of  four 
rudimentary  vertebrae;  the  number  may  however  be  increased  to  five  or  diminished 
to  three.  In  each  of  the  first  three  segments  may  be  traced  a  rudimentary  body 
and  articular  and  transverse  processes;  the  last  piece  (sometimes  the  third)  is  a 
mere  nodule  of  bone.  All  the  segments  are  destitute  of  pedicles,  laminae,  and 
spinous  processes.  The  first  is  the  largest;  it  resembles  the  lowest  sacral  vertebra, 
and  often  exists  as  a  separate  piece;  the  last  three  diminish  in  size  from  above 
(downward,  and  are  usually  fused  with  one  another. 

Surfaces. — ^The  anterior  surface  is  slightly  concave,  and  marked  with  three  trans- 
verse grooves  which  indicate  the  junctions  of  the  different  segments.  It  gives 
attachment  to  the  anterior  sacrococcygeal  ligament  and  the  Levatores  ani,  and 

H|.$upports  part  of  the  rectum.    The  posterior  surface  is  convex,  marked  by  transverse 

^"  grooves  similar  to  those  on  the  anterior  surface,  and  presents  on  either  side  a  linear 
row  of  tubercles,  the  rudimentary  articular  processes  of  the  coccygeal  vertebrae. 
3f  these,  the  superior  pair  are  large,  and  are  called  the  coccygeal  comua;  they 
project  upward,  and  articulate  with  the  cornua  of  the  sacrum,  and  on  either  side 
complete  the  foramen  for  the  transmission  of  the  posterior  division  of  the  fifth 
sacral  nerve. 

Borders. — ^The  lateral  borders  are  thin,  and  exhibit  a  series  of  small  eminences, 
which  represent  the  transverse  processes  of  the  coccygeal  vertebrae.  Of  these, 
the  first  is  the  largest;  it  is  flattened  from  before  backward,  and  often  ascends 
to  join  the  lower  part  of  the  thin  lateral  edge  of  the  sacrum,  thus  completing  the 
foramen  for  the  transmission  of  the  anterior  division  of  the  fifth  sacral  nerve; 
the  others  diminish  in  size  from  above  downward,  and  are  often  wanting.  The 
borders  of  the  coccyx  are  narrow,  and  give  attachment  on  either  side  to  the  sacro- 
tuberous  and  sacrospinous  ligaments,  to  the  Coccygeus  in  front  of  the  ligaments, 
and  to  the  Glutaeus  maximus  behind  them. 

jM ,   Base. — The  base  presents  an  oval  surface  for  articulation  with  the  sacrum. 

^1 '  Apex. — The  apex  is  rounded,  and  has  attached  to  it  the  tendon  of  the  Sphincter 
ani  externus.    It  may  be  bifid,  and  is  sometimes  deflected  to  one  or  other  side. 

■  Ossification  of  the  Vertebral  Column. — Each  cartilaginous  vertebra  isossified  from  three  primary 
centers  (Fig.  101),  two  for  the  vertebral  arch  and  one  for  the  body.'  Ossification  of  the  vertebral 
arches  begins  in  the  upper  cervical  vertebrae  about  the  seventh  or  eighth  week  of  fetal  hfe,  and  grad- 
ually extends  down  the  column.  The  ossific  granules  first  appear  in  the  situations  where  the  trans- 
verse processes  afterward  project,  and  spread  backward  to  the  spinous  process  forward  into  the 
pedicles,  and  lateralward  into  the  transverse  and  articular  processes.  Ossification  of  thebodies  begins 
about  the  eighth  week  in  the  lower  thoracic  region,  and  subsequently  extends  upward  and  down- 
ward along  the  column.  The  center  for  the  body  does  not  give  rise  to  the  whole  of  the  body  of 
the  adult  vertebra,  the  postero-lateral  portions  of  which  are  ossified  by  extensions  from  the  verte- 
^bral  arch  centers.    The  body  of  the  vertebra  during  the  first  few  years  of  life  shows,  therefore, 

!».*  u  ^^"^bra  is  occasionally  found  in  which  the  body  consists  of  two  lateral  portions — a  condition  which  proves  that 
I  Be  body  IS  sometimes  ossified  from  two  primary  centers,  one  on  either  side  of  the  middle  line. 


112 


OSTEOLOGY 


two  synchondroses,  neurocentral  synchondroses,  tr 
the  three  centers  (Fig.  102).    In  the  thoracic  region, 

Fig.  101. — Ossification  of  a  vertebra 
By  3  primary  centers 

1  for  body  {Sth  week) 


I 


Ifor  each  vertebral  arch  [llh  or  Sth  week) 

Fig.  102. 
By  3  secondary  centers 


Neurocentral 
synchondrosis 


1  for  each 
trans,  process 
16th  year 


aversing  it  along  the  planes  of  junction  of 
the  facets  for  the  heads  of  the  ribs  lie  behhid 
the  neurocentral  synchondroses  and 
are  ossified  from  the  centers  for  tlie 
vertebral  arch.  At  birth  the  vertebra 
consists  of  three  pieces,  the  body  and 
the  halves  of  the  vertebral  arch.  Dur- 
ing the  first  year  the  halves  of  tlie 
arch  unite  behind,  union  taking  place 
first  in  the  lumbar  region  and  them 
extending  upward  through  the  thoracic 
and  cervical  regions.  About  the  third 
year  the  bodies  of  the  upper  cervical 
vertebrae  are  joined  to  the  arches  on 
either  side;  in  the  lower  lumbar  verte- 
brae the  union  is  not  completed  until  the 
sixth  year.     Before  puberty,  no  other 

Additional  centers 
for  costal  elements  * 


At  birth 


1  for  spinous  process  (16fA  year) 

Fig.  103. 
By  2  additional  plates 

1  for  upper  surface' 
of  body 

1  for  under  surface 
of  body 


I6th  year 


Fig.  104.— Atlas. 


By  3  centers 


for  anter.  arch  {end  of  1st  year) 
\  llh  week 


_1  for  each 
lateral  mass 


Fig.  105.— Axis. 


By  7  centers 


2nd  year 


6th  month 
1  for  each  vertebral  arch  (7  th 

or  Sth  week) 
1  for  body  (4th  month) 
1  for  under  surface  of  body 


a 


Fig.  106. — Lumbar  vertebra. 


2  additional  centers  for  mammillary  processes 


Fig.  107 


At  ^  yrs. 


Fig.  108 


Two  epiphysial  plates 
for  each  lateral  surface  * 


At 
25th  year 


Fig.   107-109. — Ossification  of  the  sacrum. 


changes  occur,  excepting  a  gradual  increase  of  these  primary  centers,  the  upper  and  under  sur- 
faces of  the  bodies  and  the  ends  of  the  transverse  and  spinous  processes  being  cartilaginous. 


I 


THE  SACRAL  AND  COCCYGEAL  VERTEBRA 


113 


About  the  sixteenth  year  (Fig.  102),  five  secondary  centers  appear,  one  for  the  tip  of  each  transverse 
process,  one  for  the  extremity  of  the  spinous  process,  one  for  the  upper  and  one  for  the  lower 
surface  of  the  body  (Fig.  103).    These  fuse  with  the  rest  of  the  bone  about  the  age  of  twenty-five. 

Exceptions  to  this  mode  of  development  occur  in  the  first,  second,  and  seventh  cervical  verte- 
bra;, and  in  the  lumbar  vertebrae. 

Atlas.^ — The  atlas  is  usually  ossified  from  three  centers  (Fig.  104).  Of  these,  one  appears  in 
each  lateral  mass  about  the  seventh  week  of  fetal  life,  and  extends  backward;  at  birth,  these 
portions  of  bone  are  separated  from  one  another  behind  by  a  narrow  interval  filled  with  cartilage. 
Between  the  third  and  fourth  years  they  unite  either  directly  or  through  the  medium  of  a  separate 
center  developed  in  the  cartilage.  At  birth,  the  anterior  arch  consists  of  cartilage;  in  this  a 
separate  center  appears  about  the  end  of  the  first  year  after  birth,  and  joins  the  lateral  masses 
from  the  sixth  to  the  eighth  year — the  lines  of  union  extending  across  the  anterior  portions  of 
the  superior  articular  facets.  Occasionally  there  is  no  separate  center,  the  anterior  arch  being 
formed  by  the  forward  extension  and  ultimate  junction  of  the  two  lateral  masses;  sometimes 
this  arch  is  ossified  from  two  centers,  one  on  either  side  of  the  middle  line. 

Epistropheus  or  Axis. — The  axis  is  ossified  from  five  primary  and  two  secondary  centers  (Fig. 
105).  The  body  and  vertebral  arch  are  ossified  in  the  same  manner  as  the  corresponding  parts 
in  the  other  vertebrae,  viz.,  one  center  for  the  body,  and  two  for  the  vertebral  arch.  The  centers 
for  the  arch  appear  about  the  seventh  or  eighth  week  of  fetal  life,  that  for  the  body  about  the 
fc  irth  or  fifth  month.  The  dens  or  odontoid  process  consists  originally  of  a  continuation  upward 
of  the  cartilaginous  mass,  in  which  the  lower  part  of  the  body  is  formed.  About  the  sixth  month 
of  fetal  life,  two  centers  make  their  appearance  in  the  base  of  this  process:  they  are  placed 
laterally,  and  join  before  birth  to  form  a  conical  bilobed  mass  deeply  cleft  above;  the  interval 
between  the  sides  of  the  cleft  and  the  summit  of  the  process  is  formed  by  a  wedge-shaped  piece 
of  cartilage.  The  base  of  the  process  is  separated  from  the  body  by  a  cartilaginous  disk,  which 
gradually  becomes  ossified  at  its  circumference,  but  remains  cartilaginous  in  its  center  until 
advanced  age.  In  this  cartilage,  rudiments  of  the  lower  epiphysial  lamella  of  the  atlas  and 
the  upper  epiphysial  lamella  of  the  axis  may  sometimes  be  found.  The  apex  of  the  odontoid 
process  has  a  separate  center  which  appears  in  the  second  and  joins  about  the  twelfth  year;  this 
is  the  upper  epiphysial  lamella  of  the  atlas.  In  addition  to  these  there  is  a  secondary  center  for 
a  thin  epiphysial  plate  on  the  under  surface  of  the  body  of  the  bone. 

The  Seventh  Cervical  Vertebra. — The  anterior  or  costal  part  of  the  transverse  process  of  this 
vertebra  is  sometimes  ossified  from  a  separate  center  which  appears  about  the  sixth  month  of 
fetal  life,  and  joins  the  body  and  posterior  part  of  the  transverse  process  between  the  fifth  and 
sixth  years.  Occasionally  the  costal  part  persists  as  a  separate  piece,  and,  becoming  lengthened 
lateralward  and  forward,  constitutes  what  is  known  as  a  ceruical  rib.  Separate  ossific  centers 
have  also  been  found  in  the  costal  processes  of  the  fourth,  fifth,  and  sixth  cervical  vertebrae. 

Lumbar  Vertebrae. — The  lumbar  vertebrae  (Fig.  106)  have  each  two  additional  centers,  for 
[the  mammillary  processes.  The  transverse  process  of  the  first  lumbar  is  sometimes  developed  as 
a  separate  piece,  which  may  remain  permanently  ununited  with  the  rest  of  the  bone,  thus  form- 
ing a  lumbar  rib — a  peculiarity,  however, 


Center  for 
neural  a 


Center  for 
neural  arch. 


N 


jOostal 
element. 


body. 


Lateral 
epiphysis. 

Fig.  110. — Base  of  young  sacrum 


Lateral 
epiphysis. 


^ 


rarely  met  with. 

Sacrum  (Figs.  107  to  110).— The  body 
of  each  sacral  vertebra  is  ossified  from  a 
primary  center  and  tivo  epiphysial  plates, 
one  for  its  upper  and  another  for  its  under 
surface,  while  each  vertebral  arch  is  ossi- 
fied from  two  centers. 

The  anterior  portions  of  the  lateral  parts 
have  six  additional  centers,  two  for  each 
of  the  first  three  vertebrae;  these  represent 
the  costal  elements,  and  make  their  ap- 
pearance above  and  lateral  to  the  anterior 
sacral  foramina  (Figs.  107,  108). 

On  each  lateral  surface  two  epiphysial  plates  are  developed  (Figs.  109,  1 10) :  one  for  the  auric- 
ular surface,  and  another  for  the  remaining  part  of  the  thin  lateral  edge  of  the  bone.^ 

Periods  of  Ossification. — About  the  eighth  or  ninth  week  of  fetal  life,  ossification  of  the 
central  part  of  the  body  of  the  first  sacral  vertebra  commences,  and  is  rapidly  foUowed  by  deposit 
of  ossific  matter  in  the  second  and  third ;  ossification  does  not  commence  in  the  bodies  of  the 
lower  two  segments  imtil  between  the  fifth  and  eighth  months  of  fetal  hfe.     Between  the  sixth 

'  The  ends  of  the  spinous  processes  of  the  upper  three  sacral  vertebrae  are  sometimes  developed  from  separate 
epiphyses,  and  Fawcett  (Anatomischer  Anzeiger,  1907,  Band  xxx)  states  that  a  number  of  epiphysial  nodules  may  be 
seen  in  the  sacrum  at  the  age  of  eighteen  years.  These  are  distributed  as  follows:  One  for  each  of  the  mammillary  pro- 
cesses of  the  first  sacral  vertebra ;  twelve — six  on  either  side — in  connection  with  the  costal  elements  (two  each  for  the  first 
and  second  and  one  each  for  the  third  and  fourth)  and  eight  for  the  transverse  processes— four  on  either  side — one  each 
for  the  first,  third,  fourth,  and  fifth.  He  is  further  of  opinion  that  the  lower  part  of  each  lateral  surface  of  the  sacrum 
is  formed  by  the  extension  and  union  of  the  third  and  fourth  "costal"  and  fourth  and  fifth  "transverse"  epiphyses. 


■ 


114  ^^^^^^^        OSTEOLOGY 


and  eighth  months  ossification  of  the  vertebral  arches  takes  place;  and  about  the  same  time  the 
costal  centers  for  the  lateral  parts  make  their  appearance.  The  junctions  of  the  vertebral 
arches  with  the  bodies  take  place  in  the  lower  vertebrae  as  early  as  the  second  year,  but  are  not 
effected  in  the  uppermost  until  the  fifth  or  sixth  year.  About  the  sixteenth  year  the  epiphysial 
plates  for  the  upper  and  under  surfaces  of  the  bodies  are  formed;  and  between  the  eighteenth  and 
twentieth  years,  those  for  the  lateral  surfaces  make  their  appearance.  The  bodies  of  the  sacral 
vertebrae  are,  during  early  life,  separated  from  each  other  by  intervertebral  fibrocartilages,  but 
about  the  eighteenth  year  the  two  lowest  segments  become  united  by  bone,  and  the  process  of 
bony  union  gradually  extends  upward,  with  the  result  that  between  the  twenty-fifth  and  thirtieth 
years  of  life  all  the  segments  are  united.  On  examining  a  sagittal  section  of  the  sacrum,  the  situa- 
tions of  the  intervertebral  fibrocartilages  are  indicated  by  a  series  of  oval  cavities  (Fig.  99). 

Coccyx. — The  coccyx  is  ossified  from  four  centers,  one  for  each  segment.  The  ossific  nuclei 
make  their  appearance  in  the  following  order:  in  the  first  segment  between  the  first  and  fourth 
years;  in  the  second  between  the  fifth  and  tenth  years;  in  the  third  between  the  tenth  and  fifteenth 
years;  in  the  fourth  between  the  fourteenth  and  twentieth  years.  As  age  advances,  the  segments 
unite  with  om  another,  the  union  between  the  first  and  second  segments  being  frequently  delayed 
until  after  the  age  of  twenty-five  or  thirty.  At  a  late  period  of  life,  especially  in  females,  the  coccyx 
often  fuses  with  the  sacrum. 

THE  VERTEBRAL  COLUMN  AS  A  WHOLE. 

The  vertebral  column  is  situated  in  the  median  line,  as  the  posterior  part  of  the 
trunk;  its  average  length  in  the  male  is  about  71  cm.  Of  this  length  the  cervical 
part  measures  12.5  cm.,  the  thoracic  about  28  cm.,  the  lumbar  18  cm.,  and  the 
sacrum  and  coccyx  12.5  cm.     The  female  column  is  about  61  cm.  in  length. 

Curves.- — Viewed  laterally  (Fig.  Ill),  the  vertebral  column  presents  several 
curves,  which  correspond  to  the  different  regions  of  the  column,  and  are  called 
cervical,  thoracic,  lumbar,  and  pelvic.  The  cervical  curve,  convex  forward,  begins 
at  the  apex  of  the  odontoid  process,  and  ends  at  the  middle  of  the  second  thoracic 
vertebra;  it  is  the  least  marked  of  all  the  curves.  The  thoracic  curve,  concave  for- 
ward, begins  at  the  middle  of  the  second  and  ends  at  the  middle  of  the  twelfth 
thoracic  vertebra.  Its  most  prominent  point  behind  corresponds  to  the  spinous 
process  of  the  seventh  thoracic  vertebra.  The  lumbar  curve  is  more  marked  in 
the  female  than  in  the  male;  it  begins  at  the  middle  of  the  last  thoracic  vertebra, 
and  ends  at  the  sacrovertebral  angle.  It  is  convex  anteriorly,  the  convexity  of 
the  lower  three  vertebrse  being  much  greater  than  that  of  the  upper  two.  The 
pelvic  curve  begins  at  the  sacrovertebral  articulation,  and  ends  at  the  point  of  the 
coccyx;  its  concavity  is  directed  downward  and  forward.  The  thoracic  and  pelvic 
curves  are  termed  primary  curves,  because  they  alone  are  present  during  fetal  life. 
The  cervical  and  lumbar  curves  are  compensatory  or  secondary,  and  are  developed 
after  birth,  the  former  when  the  child  is  able  to  hold  up  its  head  (at  three  or  four 
months),  and  to  sit  upright  (at  nine  months),  the  latter  at  twelve  or  eighteen 
months,  when  the  child  begins  to  walk. 

The  vertebral  column  has  also  a  slight  lateral  curvature,  the  convexity  of  which 
is  directed  toward  the  right  side.  This  may  be  produced  by  muscular  action, 
most  persons  using  the  right  arm  in  preference  to  the  left,  especially  in  making 
long-continued  efforts,  when  the  body  is  curved  to  the  right  side.  In  support  of 
this  explanation  it  has  been  found  that  in  one  or  two  individuals  who  were  left- 
handed,  the  convexity  was  to  the  left  side.  By  others  this  curvature  is  regarded  as 
being  produced  by  the  aortic  arch  and  upper  part  of  the  descending  thoracic 
aorta — a  view  which  is  supported  by  the  fact  that  in  cases  where  the  viscera  are 
transposed  and  the  aorta  is  on  the  right  side,  the  convexity  of  the  curve  is 
directed  to  the  left  side. 

Surfaces. — Anterior  Surface. — When  viewed  from  in  front,  the  width  of  the  bodies 
of  the  vertebrse  is  seen  to  increase  from  the  second  cervical  to  the  first  thoracic; 
there  is  then  a  slight  diminution  in  the  next  three  vertebrse;  below  this  there 
is  again  a  gradual  and  progressive  increase  in  width  as  low  as  the  sacrovertebral 
angle.     From  this  point  there  is  a  rapid  diminution,  to  the  apex  of  the  coccyx. 


I 


I 


THE  VERTEBRAL  COLUMN  AS  A  WHOLE 


115 


I 


Posterior  Surface. — The  posterior  surface 
of  the  vertebral  cokimn  presents  in  the 
median  line  the  spinous  processes.  In  the 
cervical  region  (with  the  exception  of  the 
second  and  seventh  vertebrae)  these  are 
short  and  horizontal,  with  bifid  extremities. 
In  the  upper  part  of  the  thoracic  region 
they  are  directed  obliquely  downward;  in 
the  middle  they  are  almost  vertical,  and  in 
the  lower  part  they  are  nearly  horizontal. 
In  the  lumbar  region  they  are  nearly  hori- 
zontal. The  spinous  processes  are  separated 
by  considerable  intervals  in  the  lumbar 
region,  by  narrower  intervals  in  the  neck, 
and  are  closely  approximated  in  the  middle 
of  the  thoracic  region.  Occasionally  one  of 
,  these  processes  deviates  a  little  from  the 
median  line — a  fact  to  be  remembered  in 
practice,  as  irregularities  of  this  sort  are 
attendant  also  on  fractures  or  displacements 
of  the  vertebral  column.  On  either  side  of 
the  spinous  processes  is  the  vertebral  groove 
formed  by  the  laminae  in  the  cervical  and 
lumbar  regions,  where  it  is  shallow,  and  by 
the  laminae  and  transverse  processes  in  the 
thoracic  region,  where  it  is  deep  and  broad ; 
these  grooves  lodge  the  deep  muscles  of  the 
back.  Lateral  to  the  vertebral  grooves  are 
the  articular  processes,  and  still  more  later- 
ally the  transverse  processes.  In  the  tho- 
racic region,  the  transverse  processes  stand 
backward,  on  a  plane  considerably  behind 
that  of  the  same  processes  in  the  cervical 
and  lumbar  regions.  In  the  cervical  region, 
I  the  trans^•erse  processes  are  placed  in  front 
'of  the  articular  processes,  lateral  to  the 
pedicles  and  between  the  intervertebral 
foramina.  In  the  thoracic  region  they  are 
posterior  to  the  pedicles,  intervertebral 
foramina,  and  articular  processes.  In  the 
lumbar  region  they  are  in  front  of  the 
articular  processes,  but  behind  the  inter- 
vertebral foramina. 

Lateral  Surfaces. — ^The  lateral  surfaces  are 
separated  from  the  posterior  surface  by  the 
articular  processes  in  the  cervical  and  lum- 
bar regions,  and  by  the  transverse  processes 
in  the  thoracic   region.    They  present,   in 
I  front,  the  sides  of  the  bodies  of  the  verte- 
I  brae,  marked  in  the  thoracic  region  by  the 
r  facets  for    articulation  with  the  heads  of 
the  ribs.     jNIore  posteriorly  are  the  inter- 
vertebral foramina,   formed  by  the  juxta- 
position of  the  vertebral  notches,  oval  in 


Fia.   111. — Lateral  view  of  the  vertebral  column. 


116 


OSTEOLOGY 


shape,  smallest  in  the  cervical  and  upper  part  of  the  thoracic  regions,  and  gradually] 
increasing  in  size  to  the  last  lumbar.    They  transmit  the  spinal  nerves  and  'ar«3 
situated  between  the  transverse  processes  in  the  cervical  region,  and  in  front  of 
them  in  the  thoracic  and  lumbar  regions. 

Vertebral  Canal. — The  vertebral  canal  follows  the  different  curves  of  the  column; 
it  is  large  and  triangular  in  those  parts  of  the  column  which  enjoy  the  greatest 
freedom  of  movement,  viz.,  the  cervical  and  lumbar  regions;  and  is  small  and 
rounded  in  the  thoracic  region,  where  motion  is  more  limited. 

Abnormalities. — Occasionally  the  coalescence  of  the  laminae  is  not  completed,  and  conse- 
quently a  cleft  is  left  in  the  arches  of  the  vertebrae,  through  which  a  protrusion  of  the  spinal 
membranes  (dura  mater  and  arachnoid),  and  generally  of  the  medulla  spinaUs  itself,  takes  place, 
constituting  the  malformation  known  as  spina  bifida.  This  condition  is  most  common  in  the 
lumbosacral  region,  but  it  may  occur  in  the  thoracic  or  cervical  region,  or  the  arches  throughout 
the  whole  length  of  the  canal  may  remain  incomplete. 


First  thoracic 


Fig.  112. — The  thorax  from  in  front.     (Spalteholz.) 

THE   THORAX. 


The  skeleton  of  the  thorax  or  chest  (Figs.  112,  113,  114)  is  an  osseo-cartilaginous 
cage,  containing  and  protecting  the  principal  organs  of  respiration  and  circulation. 


I 


THE  THORAX 


117 


It  is  conical  in  shape,  being  narrow  above  and  broad  below,  flattened  from  before 
backward,  and  longer  behind  than  in  front.  It  is  somewhat  reniform  on  trans- 
verse section  on  account  of  the  projection  of  the  vertebral  bodies  into  the  cavity. 


First  thoracic 


Fia.  113. — The  thorax  from  behind.     (Spalteholz.) 


Boundaries. — The  posterior  surface  is  formed  by  the  twelve  thoracic  vertebrae 
and  the  posterior  parts  of  the  ribs.  It  is  convex  from  above  downward,  and  pre- 
sents on  either  side  of  the  middle  line  a  deep  groove,  in  consequence  of  the  lateral 
and  backward  direction  which  the  ribs  take  from  their  vertebral  extremities  to 
their  angles.  The  anterior  surface,  formed  by  the  sternum  and  costal  cartilages, 
is  flattened  or  slightly  convex,  and  inclined  from  above  downward  and  forward. 
The  lateral  surfaces  are  convex;  they  are  formed  by  the  ribs,  separated  from 
jcach  other  by  the  intercostal  spaces,  eleven  in  number,  which  are  occupied  by 
fthe  Intercostal  muscles  and  membranes. 

The  upper  opening  of  the  thorax  is  Teniform  in  shape,  being  broader  from  side 
ko  side  than  from  before  backward.  It  is  formed  by  the  first  thoracic  vertebra 
[behind,  the  upper  margin  of  the  sternum  in  front,  and  the  first  rib  on  either  side. 


118 


OSTEOLOGY 


It"  slopes  downward  and  forward,  so  that  the  anterior  part  of  the  opening  is  on  a 
lower  level  than  the  posterior.  Its  antero-posterior  diameter  is  about  5  cm.,  and 
its  transverse  diameter  about  10  em.  The  lower  opening  is  formed  by  the  twelftli 
thoracic  vertebra  behind,  by  the  eleventh  and  twelfth  ribs  at  the  sides,  and  in  front 
by  the  cartilages  of  the  tenth,  ninth,  eighth,  and  seventh  ribs,  which  ascend  on 
either  side  and  form  an  angle,  the  subcostal  angle,  into  the  apex  of  which  the 


First  thoTi 


■Sternum 


Twelfth  thoracic' 


First  lumbar 


Fig.  114. — The  thorax  from  the  right.     (Spalteholz.) 


xiphoid  process  projects.  The  lower  opening  is  wider  transversely  than  from 
before  backward,  and  slopes  obliquely  downward  and  backward,  it  is  closed  by 
the  diaphragm  which  forms  tlie  floor  of  the  thorax. 


The  thorax  of  the  female  differs  from  that  of  the  male  as  follows:  1.  Its  capacity  is  less.  2. 
The  sternum  is  shorter.  3.  The  upper  margin  of  the  sternum  is  on  a  level  with  the  lower  part 
of  the  body  of  the  third  thoracic  vertebra,  whereas  in  the  male  it  is  on  a  level  with  the  lower 
part  of  the  body  of  the  second.  4.  The  upper  ribs  are  more  movable,  and  so  allow  a  greater 
enlargement  of  the  upper  part  of  the  thorax. 


THE  STERNUM 


The  Sternum  (Breast  Bone). 


119 


Tlie  sternum  (F'igs.  115  to  117)  is  an  elongated,  flattened  bone,  forming  the 
middle  portion  of  the  anterior  wall  of  the  thorax.  Its  upper  end  supports  the 
clavicles,  and  its  margins  articulate  with  the  cartilages  of  the  first  seven  pairs 


STEENOCLEIDOMASTOIDEUS 
S0BCLAVIDS     \  '^i<ffulaf 


Fig.   115. — Anterior  surface  of  sternum  and  costa   cartilages. 


of  ribs.  It  consists  of  three  parts,  named  from  above  downward,  the  manubrium, 
the  body  or  gladiolus,  and  the  xiphoid  process ;  in  early  life  the  body  consists  of  four 
segments  or  sternehroB.  In  its  natural  position  the  inclination  of  the  bone  is  oblique 
from  above,  downward  and  forward.     It  is  slightly  convex  in  front  and  concave 


i 


120 


OSTEOLOGY 


I 


behind;  broad  above,  becoming  narrowed  at  the  point  where  the  manubrium  joins 
the  body,  after  which  it  again  widens  a  little  to  below  the  middle  of  the  body, 
and  then  narrows  to  its  lower  extremity.  Its  average  length  in  the  adult  is  about 
17  cm.,  and  is  rather  greater  in  the  male  than  in  the  female. 

Manubrium  {manubrium  sterni). — The  manubrium  is  of  a  somewhat  quad- 
rangular form,  broad  and  thick  above,  narrow  below  at  its  junction  with  the  body. 

Surfaces. — Its  anterior  surface,  convex  from  side  to  side,  concave  from  above 
downward,  is  smooth,  and  affords  attachment  on  either  side  to  the  sternal 
origins  of  the  Pectoralis  major  and  Sternocleidomastoideus.  Sometimes  the 
ridges  limiting  the  attachments  of  these  muscles  are  very  distinct.  Its  posterior 
surface,  concave  and  smooth,  affords  attachment  on  either  side  to  the  Sterno- 
hyoideus  and  Sternothyreoideus. 


For  1st 
^-L  costal 
cartilage 


Sternal 
angle 


Xiphoid  process 


Fig.   116. — Posterior  surface  of  aternum. 


Articular  surface 
for  clavicle 

Depression  for 

lut  costal  cartilage 

Manvhrium 


Demifacets  for  2nd  costal 
cartilage 


Facet  fpY  Zrd  costal  cartilage 
Body 


Facet  for  Atli  costal  cartilage 

Facet  for  5th  costal  cartilage 

-Facet  for  6th  costal  cartilage 
-Facet  for  7th  costal  cartilage 
Xiphoid  process 


Fig.   117. — Lateral  border  of  sternum. 


Borders. — The  superior  border  is  the  thickest  and  presents  at  its  center  the  jugular 
or  presternal  notch ;  on  either  side  of  the  notch  is  an  oval  articular  surface,  directed 
upward,  backward,  and  lateralward,  for  articulation  with  the  sternal  end  of  the 
clavicle.  The  inferior  border,  oval  and  rough,  is  covered  in  a  fresh  state  with  a 
thin  layer  of  cartilage,  for  articulation  with  the  body.  The  lateral  borders  are  each 
marked  above  by  a  depression  for  the  first  costal  cartilage,  and  below  by  a  small 
facet,  which,  with  a  similar  facet  on  the  upper  angle  of  the  body,  forms  a  notch 
for  the  reception  of  the  costal  cartilage  of  the  second  rib.  Between  the  depression 
for  the  first  costal  cartilage  and  the  demi-facet  for  the  second  is  a  narrow,  curved 
edge,  which  slopes  from  above  downward  and  medialward. 

Body  {corpus  sterni;  gladiolus) . — The  body,  considerably  longer,  narrower,  and 
thinner  than  the  manubrium,  attains  its  greatest  breadth  close  to  the  lower  end. 

Surfaces. — Its  anterior  surface  is  nearly  flat,  directed  upward  and  forward, 
and  marked  by  three  transverse  ridges  which  cross  the  bone  opposite  the  third, 


i 


THE  STERNUM  ^^^^^M"  121 


I 


fourth,  and  fifth  articular  depressions.^  It  affords  attachment  on  either  side  to 
the  sternal  origin  of  the  Pectoralis  major.  At  the  junction  of  the  third  and  fourth 
jiieces  of  the  body  is  occasionally  seen  an  orifice,  the  sternal  foramen,  of  varying 
size  and  form.  The  posterior  surface,  slightly  concave,  is  also  marked  by  three 
transverse  lines,  less  distinct,  however,  than  those  in  front;  from  its  lower  part, 
on  either  side,  the  Transversus  thoracis  takes  origin. 

Borders. — The  superior  border  is  oval  and  articulates  with  the  manubrium,  the 
junction  of  the  two  forming  the  sternal  angle  (anguhis  Ludovici").  The  inferior 
border  is  narrow,  and  articulates  with  the  xiphoid  process.  Each  lateral  border 
(Fig.  117),  at  its  superior  angle,  has  a  small  facet,  which  with  a  similar  facet  on 
the  manubrium,  forms  a  cavity  for  the  cartilage  of  the  second  rib;  below  this 
are  four  angular  depressions  which  receive  the  cartilages  of  the  third,  fourth, 
fifth,  and  sixth  ribs,  while  the  inferior  angle  has  a  small  facet,  which,  with  a  cor- 
responding one  on  the  xiphoid  process,  forms  a  notch  for  the  cartilage  of  the  seventh 
rib.  These  articular  depressions  are  separated  by  a  series  of  curved  interarticular 
intervals,  which  diminish  in  length  from  above  downward,  and  correspond  to 
the  intercostal  spaces.  Most  of  the  cartilages  belonging  to  the  true  ribs,  as  will 
be  seen  from  the  foregoing  description,  articulate  with  the  sternum  at  the  lines 
of  junction  of  its  primitive  component  segments.  This  is  well  seen  in  many  of 
the  lower  animals,  where  the  parts  of  the  bone  remain  ununited  longer  than  in 
man. 

Xiphoid  Process  {processus  xiphoideus;  ensiform  or  xiphoid  appendix). — The 
xiphoid  process  is  the  smallest  of  the  three  pieces:  it  is  thin  and  elongated, 
cartilaginous  in  structure  in  youth,  but  more  or  less  ossified  at  its  upper  part  in 
the  adult. 

Surfaces. — Its  anterior  surface  affords  attachment  on  either  side  to  the  anterior 
costoxiphoid  ligament  and  a  small  part  of  the  Rectus  abdominis;  its  posterior  sur- 
face, to  the  posterior  costoxiphoid  ligament  and  to  some  of  the  fibers  of  the  dia- 
phragm and  Transversus  thoracis,  its  lateral  borders,  to  the  aponeuroses  of  the 
abdominal  muscles.  Above,  it  articulates  with  the  lower  end  of  the  body,  and 
on  the  front  of  each  superior  angle  presents  a  facet  for  part  of  the  cartilage  of  the 
seventh  rib;  below,  by  its  pointed  extremity,  it  gives  attachment  to  the  linea 
alba.  The  xiphoid  process  varies  much  in  form;  it  may  be  broad  and  thin,  pointed, 
bifid,  perforated,  curved,  or  deflected  considerably  to  one  or  otner  side. 

Structure. — The  sternum  is  composed  of  highly  vascular  cancellous  tissue,  covered  by  a  thin 
layer  of  compact  bone  which  is  thickest  in  the  manubrium  between  the  articular  facets  for  the 
clavicles. 

Ossification. — The  sternum  originally  consists  of  two  cartilaginous  bars,  situated  one  on  either 
side  of  the  median  plane  and  connected  with  the  cartilages  of  the  upper  nine  ribs  of  its  own  side. 
These  two  bars  fuse  with  each  other  along  the  middle  line  to  form  the  cartilaginous  sternum  which 
is  ossified  from  six  centers:  one  for  the  manubrium,  four  for  the  body,  and  one  for  the  xiphoid 
process  (Fig.  118).  The  ossific  centers  appear  in  the  intervals  between  the  articular  depressions 
for  the  costal  cartilages,  in  the  following  order:  in  the  manubrium  and  first  piece  of  the  body, 
during  the  sixth  month;  in  the  second  and  third  pieces  of  the  body,  during  the  seventh  month  of 
fetal  life;  in  its  fourth  piece,  during  the  first  year  after  birth;  and  in  the  xiphoid  process,  between 
the  fifth  and  eighteenth  years.  The  centers  make  their  appearance  at  the  upper  parts  of  the  seg- 
ments, and  proceed  gradually  downward.^  To  these  may  be  added  the  occasional  existence  of 
two  small  episternal  centers,  which  make  their  appearance  one  on  either  side  of  the  jugular  notch; 
they  are  probably  vestiges  of  the  episternal  bone  of  the  monotremata  and  lizards.  Occasionally 
some  of  the  segments  are  formed  from  more  than  one  center,  the  number  and  position  of  which 
vary  (Fig.  120).    Thus,  the  first  piece  may  have  two,  three,  or  even  six  centers.    When  two  are 

'  Paterson  (The  Human  Sternum,  1904),  who  examined  521  specimens,  points  out  that  these  ridges  are  altogether 
absent  in  26.7  per  cent. ;  that  in  69  per  cent,  a  ridge  exists  opposite  the  third  costal  attachment;  in  39  per  cent,  opposite 
the  fourth;  and  in  4  per  cent,  only,  opposite  the  fifth. 

2  Named  after  the  French  surgeon  Antoine  Louis,  1723-1792.  The  Latin  name  anjulus  Ludovici  is  not  infrequently 
mistranslated  into  English  as  "the  angle  of  Ludwig. " 

'  Out  of  141  sterna  between  the  time  of  birth  and  the  age  of  sixteen  years,  Paterson  (,op.  cit.)  found  the  fourth  or 
lowest  center  for  the  body  present  only  in  thirty-eight  cases — t.  e.,  26.9  per  cent. 


122 


OSTEOLOGY 


Time 

of 

appearance 


Time 

of 
union 


In 

number  of 
centers 


In 

mode  of 


1  for  manubrium   \ 

\6lh  month 
(2) 
3\ 

*\ 

_  5     1st  year  after  birth 


4  for  body 


■  7th  month 


1  for.  xiphoid  \ 

process        f^^^  '^  ^^^^  year 


Fig.   118. — O-ssification  of  the  sternum. 


Rarely  unite,  except  in  old  age 
Between  puberty  and  the  25th  year 

Soon  after  puberty 

Partly  cartilaginous  to  advanced  life 
FiQ.  119 


for  first  piece,  two  or  more  centers 

for  second  piece,  ustudly  one 

for  third  '\ 

,  f  ^>  placed  laterally 
forfouHh)      ^  * 

for  fifth 


Fig.   120. — Peculiaritiea. 


Arrest  of  ossification  of  lateral  ineces. 
producing  : 

Sternal  fissure,  and 


Sternal  foramen 


Fig.  121 


I 


THE  RIBS  Wl^m  123 


^ 


Wh 


present,  they  are  generally  situated  one  above  the  other,  the  upper  being  the  larger;  the  second 
piece  has  seldom  more  than  one;  the  third,  fourth,  and  fifth  pieces  are  often  formed  from  two 
centers  placed  laterally,  the  irregular  union  of  which  explains  the  rare  occurrence  of  the  sternal 
foramen  (Fig.  121),  or  of  the  vertical  fissure  which  occasionally  intersects  this  part  of  the  bone 
constituting  the  malformation  known  as  fissura  sterni;  these  conditions  are  further  explained  by 
the  manner  in  which  the  cartilaginous  sternum  is  formed.  More  rarely  still  the  upper  end  of  the 
sternum  may  be  divided  by  a  fissure.  Union  of  the  various  centers  of  the  body  begins  about 
puberty,  and  proceeds  from  below  upward  (Fig.  119) ;  by  the  age  of  twenty-five  they  are  all  imited. 
The  xiphoid  process  may  become  joined  to  the  body  before  the  age  of  thirty,  but  this  occurs 
more  frequently  after  forty;  on  the  other  hand,  it  sometimes  remains  ununited  in  old  age.  In 
advanced  life  the  manubrium  is  occasionally  joined  to  the  body  by  bone.  When  this  takes  place, 
however,  the  bony  tissue  is  generally  only  superficial,  the  central  portion  of  the  intervening 
cartilage  remaining  unossified. 

Articulations. — The  sternum  articulates  on  either  side  with  the  clavicle  and  upper  seven  costal 
cartilages. 

The  Ribs  (Costae). 

The  ribs  are  elastic  arches  of  bone,  which  form  a  large  part  of  the  thoracic 
skeleton.  They  are  twelve  in  number  oh  either  side;  but  this  number  may  be 
increased  by  the  development  of  a  cervical  or  lumbar  rib,  or  may  be  diminished 
to  eleven.  The  first  seven  are  connected  behind  with  the  vertebral  column,  and  in 
front,  through  the  intervention  of  the  costal  cartilages,  with  the  sternum  (Fig. 
115);  they  are  called  true  or  vertebro-stemal  ribs.^  The  remaining  five  are  false 
ribs ;  of  these,  the  first  three  have  their  cartilages  attached  to  the  cartilage  of  the 
rib  above  (vertebro-chondral) :  the  last  two  are  free  at  their  anterior  extremities 
and  are  termed  floating  or  vertebral  ribs.  The  ribs  vary  in  their  direction,  the 
upper  ones  being  less  oblique  than  the  lower;  the  obliquity  reaches  its  maximum 
at  the  ninth  rib,  and  gradually  decreases  from  that  rib  to  the  twelfth.  The  ribs 
are  situated  one  below  the  other  in  such  a  manner  that  spaces  called  intercostal 
spaces  are  left  between  them.  The  length  of  each  space  corresponds  to  that  of 
[the  adjacent  ribs  and  their  cartilages;  the  breadth  is  greater  in  front  than  behind, 
and  between  the  upper  than  the  lower  ribs.  The  ribs  increase  in  length  from 
the  first  to  the  seventh,  below  which  they  diminish  to  the  twelfth.  In  breadth 
they  decrease  from  above  downward;  in  the  upper  ten  the  greatest  breadth  is  at 
the  sternal  extremity. 

{  Common  Characteristics  of  the  Ribs  (Figs.  122,  123). — A  rib  from  the  middle 
of  the  series  should  be" taken  in  order  to  study  the  common  characteristics  of  these 
bones. 

Each  rib  has  two  extremities,  a  posterior  or  vertebral,  and  an  anterior  or  sternal, 
and  an  intervening  portion — the  body  or  shaft. 

Posterior  Extremity. — The  posterior  or  vertebral  extremity  presents  for  examination 
a  head,  neck,  and  tubercle. 

The  head  is  marked  by  a  kidney-shaped  articular  surface,  divided  by  a  hori- 
zontal crest  into  two  facets  for  articulation  with  the  depression  formed  on  the 
bodies  of  two  adjacent  thoracic  vertebrae;  the  upper  facet  is  the  smallier;  to  the 
crest  is  attached  the  interarticular  ligament.  ^ 

The  neck  is  the  flattened  portion  which  extends  lateralward  from  the  head;  it 
is  about  2.5  cm.  long,  and  is  placed  in  front  of  the  transverse  process  of  the 
lower  of  the  two  vertebrae  with  which  the  head  articulates.  Its  anterior  surface  is 
flat  and  smooth,  its  posterior  rough  for  the  attachment  of  the  ligament  of  the  neck, 
nd  perforated  by  numerous  foramina.  Of  its  two  borders  the  superior  presents  a 
rough  crest  (crista  colli  costoe)  for  the  attachment  of  the  anterior  costotransverse 
ligament;  its  inferior  border  is  rounded.  On  the  posterior  surface  at  the  junction 
of  the  neck  and  body,  and  nearer  the  lower  than  the  upper  border,  is  an  eminence 

_  1  Sometimes  the  eighth  rib  cartilage  articulates  with  the  sternum;  thi-s  coaditioa  occurs  more  frequently  on  the 
right  than  on  the  left  side. 


km 


124 


OSTEOLOGY 


— the  tubercle ;  it  consists  of  an  articular  and  a  non-articular  portion.    The  articuiar 
portion,  the  lower  and  more  medial  of  the  two,  presents  a  small,  oval  surface  lor 


I 


Angle 


•Costal  groove 


S 
Sf 


•Body 


Non-articular  part  of  tubercle 

Articular  part  of  tubercle 


■^ 


Fig.  122.- 


central  rib  of  the  left  side. 
Inferior  aspect. 


articulation  with  the  end  of  the  transverse  pro- 
cess of  the  lower  of  the  two  vertebrae  to  which 
the  head  is  connected.  The  non-articular  por- 
tion is  a  rough  elevation,  and  affords  attach- 
ment to  the  ligament  of  the  tubercle.  The 
tubercle  is  much  more  prominent  in  the  upper 
than  in  the  lower  ribs. 

Body. — The  body  or  shaft  is  thin  and  flat, 
with  two  surfaces,  an  external  and  an  internal ; 
and  two  borders,  a  superior  and  an  inferior. 
The  external  surface  is  convex,  smooth,  and 
marked,  a  little  in  front  of  the  tubercle,  by  a 
prominent  line,  directed  downw^ard  and  lateral- 
ward;  this  gives  attachment  to  a  tendon  of 
the  Iliocostalis,  and  is  called  the  angle.  At 
this  point  the  rib  is  bent  in  tw^o  directions, 
and  at  the  same  time  twisted  on  its  long  axis. 
If  the  rib  be  laid  upon  its  lower  border,  the 
portion  of  the  body  in  front  of  the  angle  rests 
upon  this  border,  while  the  portion  behind  the 
angle  is  bent  medial  ward  and  at  the  same 
time  tilted  upw-ard;  as  the  result  of  the  twist- 
ing, the  external  surface,  behind  the  angle, 
looks  downward,  and  in  front  of  the  angle, 
slightly  upward.  The  distance  between  the 
angle  and  the  tubercle  is  progressively  greater 
from  the  second  to  the  tenth  ribs.  The  por- 
tion between  the  angle  and  the  tubercle  is 
rounded,  rough,  and  irregular,  and  serves  for 
the  attachment  of  the  Longissimus  dorsi.  The 
internal  surface  is  concave,  smooth,  directed  a 
little  upward  behind  the  angle,  a  little  down- 
ward in  front  of  it,  and  is  marked  by  a  ridge 
which  commences  at  the  lower  extremity  of 
the  head;  this  ridge  is  strongly  marked  as  far 
as  the  angle,  and  gradually  becomes  lost  at 
the  junction  of  the  anterior  and  middle  thirds 
of  the  bone.  Between  it  and  the  inferior 
border  is  a  groove,  the  costal  groove,  for  the 
intercostal  vessels  and  nerve.  At  the  back 
part  of  the  bone,  this  groove  belongs  to  the 


I 


THE  RIBS 


125 


inferior  border,  but  just  in  front  of  the  angle,  where  it  is  deepest  and  broadest,  it  is 
on  the  internal  surface.  The  superior  edge  of  the  groove  is  rounded  and  serves 
for  the  attachment  of  an  Intercostalis  internus;  the  inferior  edge  corresponds  to 
the  lower  margin  of  the  rib,  and  gives  attachment  to  an  Intercostalis  externus. 
Within  the  groove  are  seen  the  oriifices  of  numerous  small  foramina  for  nutrient 
vessels  which  traverse  the  shaft  obliquel}'  from  before  backward.  The  superior 
border,  thick  and  rounded,  is  marked  by  an  external  and  an  internal  lip,  more 
distinct  behind  than  in  front,  which  serve  for  the  attachment  of  Intercostales 
externus  and  internus.  The  inferior  border  is  thin,  and  has  attached  to  it  an  Inter- 
costalis externus. 

Anterior  Extremity. — The  anterior  or  sternal  extremity  is  flattened,  and  presents  a 
porous,  oval,  concave  depression,  into  which  the  costal  cartilage  is  received. 

Peculiar  Ribs.— The  first,  second,  tenth,  eleventh,  and  twelfth  ribs  present 
certain  variations  from  the  common  characteristics  described  above,  and  require 
special  consideration. 

'  Demifacet  for  vertebra 

Jnterarticular  crest 

Demifacet  for  vertebra 


A  central  rib  of  the  left  aide,  viewed  from  behind. 


First  Rib. — The  first  rib  (Fig.  124)  is  the  most  curved  and  usually  the  shortest 
)f  all  the  ribs;  it  is  broad  and  flat,  its  surfaces  looking  upward  and  downward, 

■  md  its  borders  inward  and  outward.  The  head  is  small,  rounded,  and  possesses 
-felly  a  single  articular  facet,  for  articulation  with  the  body  of  the  first  thoracic 
'  \^ertebra.  The  neck  is  narrow  and  rounded.  The  tubercle,  thick  and  prominent, 
s  placed  on  the  outer  border.  There  is  no  angle,  but  at  the  tubercle  the  rib  is 
slightly  bent,  with  the  convexity  upward,  so  that  the  head  of  the  bone  is  directed 
downward.  The  upper  surface  of  the  body  is  marked  by  two  shallow  grooves, 
separated  from  each  other  by  a  slight  ridge  prolonged  internally  into  a  tubercle, 
the  scalene  tubercle,  for  the  attachment  of  the  Scalenus  anterior;  the  anterior 
groove  transmits  the  subclavian  vein,  the  posterior  the  subclavian  artery  and 
the  lowest  trunk  of  the  brachial  plexus.^  Behind  the  posterior  groove  is  a  rough 
area  for  the  attachment  of  the  Scalenus  medius.  The  under  surface  is  smooth, 
and  destitute  of  a  costal  groove.  The  outer  border  is  convex,  thick,  and  rounded, 
and  at  its  posterior  part  gives  attachment  to  the  first  digitation  of  the  Serratus 
anterior;  the  inner  border  is  concave,  thin,  and  sharp,  and  marked  about  its  center 
by  the  scalene  tubercle.  The  anterior  extremity  is  larger  and  thicker  than  that 
of  any  of  the  other  ribs. 
Second  Rib. — ^The  second  rib  (Fig.  125)  is  much  longer  than  the  first,  but  has  a 

...... .,„„...„.^, 


'  Anat.  Anzeiger,  1910,  Band  xxxvi. 


126 


OSTEOLOGY 


I 


only  feebly  marked.  The  angle  is  slight,  and  situated  close  to  the  tubercle.  Tlie 
body  is  not  twisted,  so  that  both  ends  touch  any  plane  surface  upon  which  it  may 
be  laid;  but  there  is  a  bend,  with  its  convexity  upward,  similar  to,  though  smaller 
than  that  found  in  the  first  rib.  The  body  is  not  flattened  horizontally  like  that 
of  the  first  rib.  Its  external  surface  is  convex,  and  looks  upward  and  a  little  outward ; 
near  the  middle  of  it  is  a  rough  eminence  for  the  origin  of  the  lower  part  of  the 


FiQ.   124 


Fig.  125 


Angi 


FiQ.   126 
Single  articular  facet  — 


FiQ.  127 
Single  articular  facet 


Fia.  128 
Single  articular  facet 


Figs.    124  to  128. — Peculiar  ribs. 

first  and  the  whole  of  the  second  digitation  of  the  Serratus  anterior;  behind  and 
above  this  is  attached  the  Scalenus  posterior.  The  internal  surface,  smooth,  and 
concave,  is  directed  downward  and  a  little  inward:  on  its  posterior  part  there  is 
a  short  costal  groove. 

Tenth  Rib. — ^The  tenth  rib  (Fig.  126)  has  only  a  single  articular  facet  on  its  head. 

Eleventh  and  Twelfth  Ribs. — The  eleventh  and  twelfth  ribs  (Figs.  127  and  128) 
have  each  a  single  articular  facet  on  the  head,  which  is  of  rather  large  size;  they 


I 


THE  COSTAL  CARTILAGES  ^^^K         127 


have  no  necks  or  tubercles,  and  are  pointed  at  their  anterior  ends.  The  eleventh 
has  a  slight  angle  and  a  shallow  costal  groove.  The  twelfth  has  neither;  it  is  much 
shorter  than  the  eleventh,  and  its  head  is  inclined  slightly  downward.  Sometimes 
the  twelfth  rib  is  even  shorter  than  the  first. 

Structure. — The  ribs  consist  of  liighly  vascular  cancellous  tissue,  enclosed  in  a  thin  layer  of 
compact    bone. 

Ossification. — Each  rib,  with  the  exception  of  the  last  two,  is  ossified  from  four  centers;  a 
primary  center  for  the  body,  and  three  epiphysial  centers,  one  for  the  head  and  one  each  for  the 
articular  and  non-articular  parts  of  the  tubercle.  The  eleventh  and  twelfth  ribs  have  each  only 
two  centers,  those  for  the  tubercles  being  wanting.  Ossification  begins  near  the  angle  toward  the 
end  of  the  second  month  of  fetal  life,  and  is  seen  first  in  the  sixth  and  seventh  ribs.  The  epiphyses 
for  the  head  and  tubercle  make  their  appearance  between  the  sixteenth  and  twentieth  years,  and 
are  united  to  the  body  about  the  twenty-fifth  year.  Fawcett^  states  that  "in  all  probabihty  there 
is  usually  no  epiphysis  on  the  non-articular  part  of  the  tuberosity  below  the  sixth  or  seventh  rib. 

PThe  Costal  Cartilages  (Cartilagines  Costales). 
The  costal  cartilages  (Fig.  115)  are  bars  of  hyaline  cartilage  which  serve  to 
prolong  the  ribs  forward  and  contribute  very  materially  to  the  elasticity  of  the 
walls  of  the  thorax.  The  first  seven  pairs  are  connected  with  the  sternum;  the 
next  three  are  each  articulated  with  the  lower  border  of  the  cartilage  of  the  pre- 
ceding rib;  the  last  two  have  pointed  extremities,  which  end  in  the  wall  of  the 
abdomen.  Like  the  ribs,  the  costal  cartilages  vary  in  their  length,  breadth,  and 
direction.  They  increase  in  length  from  the  first  to  the  seventh,  then  gradually 
decrease  to  the  twelfth.  Their  breadth,  as  well  as  that  of  the  intervals  between 
them,  diminishes  from  the  first  to  the  last.  They  are  broad  at  their  attachments 
to  the  ribs,  and  taper  toward  their  sternal  extremities,  excepting  the  first  two, 
which  are  of  the  same  breadth  throughout,  and  the  sixth,  seventh,  and  eighth, 
v.hich  are  enlarged  where  their  margins  are  in  contact.  They  also  vary  in  direc- 
tion: the  first  descends  a  little,  the  second  is  horizontal,  the  third  ascends  slightly, 
^,'hile  the  others  are  angular,  following  the  course  of  the  ribs  for  a  short  distance, 
find  then  ascending  to  the  sternum  or  preceding  cartilage.  Each  costal  cartilage 
I)resents  two  surfaces,  two  borders,  and  two  extremities. 

Surfaces. — The  anterior  surface  is  convex,  and  looks  forward  and  upward:  that 
of  the  first  gives  attachment  to  the  costoclavicular  ligament  and  the  Subclavius 
muscle;  those  of  the  first  six  or  seven  at  their  sternal  ends,  to  the  Pectoralis  major. 
The  others  are  covered  by,  and  give  partial  attachment  to,  some  of  the  flat  muscles 
of  the  abdomen.  The  posterior  surface  is  concave,  and  directed  backward  and 
downward;  that  of  the  first  gives  attachment  to  the  Sternothyroideus,  those  of 
the  third  to  the  sixth  inclusive  to  the  Transversus  thoracis,  and  the  six  or  seven 
inferior  ones  to  the  Transversus  abdominis  and  the  diaphragm. 

Borders. — Of  the  two  borders  the  superior  is  concave,  the  inferior  convex;  they 
afford  attachment  to  the  Intercostales  interni:  the  upper  border  of  the  sixth  gives 
attachment  also  to  the  Pectoralis  major.  The  inferior  borders  of  the  sixth,  seventh, 
eighth,  and  ninth  cartilages  present  heel-like  projections  at  the  points  of  greatest 
convexity.  These  projections  carry  smooth  oblong  facets  which  articulate  respec- 
tively with  facets  on  slight  projections  from  the  upper  borders  of  the  seventh, 
(eighth,  ninth,  and  tenth  cartilages. 

^  Extremities. — The  lateral  end  of  each  cartilage  is  continuous  with  the  osseous 
tissue  of  the  rib  to  which  it  belongs.  The  medial  end  of  the  first  is  continuous 
with  the  sternum;  the  medial  ends  of  the  six  succeeding  ones  are  rounded  and  are 
received  into  shallow  concavities  on  the  lateral  margins  of  the  sternum.  The 
medial  ends  of  the  eighth,  ninth,  and  tenth  costal  cartilages  are  pointed,  and  are 
connected  each  with  the  cartilage  immediately  above.  Those  of  the  eleventh  and 
twelfth  are  pointed  and  free.  In  old  age  the  costal  cartilages  are  prone  to  undergo 
superficial  ossification. 

1  Journal  of  Anatomy  and  Physiology,  vol.  xlv. 


■ 


128 


OSTEOLOGY 


I 


Cervical  ribs  derived  from  the  seventh  cervical  vei'tebra  (page  83)  are  of  not  infrequent  occur- 
rence, and  are  important  clinically  because  they  may  give  rise  to  obscure  nervous  or  vascular 
symptoms.  The  cervical  rib  may  be  a  mere  epiphysis  articulating  only  with  the  transverse  process 
of  the  vertebra,  but  more  commonly  it  consists  of  a  defined  head,  neck,  and  tubercle,  with  or 
without  a  body.  It  extends  lateralwaixl,  or  forward  and  lateralward,  into  the  posterior  triangle 
of  the  neck,  where  it  may  terminate  in  a  free  end  or  may  join  the  first  thoracic  rib,  the  first  costal 
cartilage,  or  the  sternum. ^  It  varies  much  in  shape,  size,  direction,  and  mobility.  If  it  ret.ch 
far  enough  forward,  part  of  the  brachial  plexus  and  the  subclavian  artery  and  vein  cross  o^er 
it,  and  are  apt  to  suffer  compression  in  so  doing.  Pressure  on  the  artery  may  obstruct  the  circula- 
tion so  much  that  arterial  thrombosis  results,  causing  gangrene  of  the  finger  tips.  Pressure  on 
the  nerves  is  commoner,  and  affects  the  eighth  cervical  and  first  thoracic  nerves,  causing  paralysis 
of  the  muscles  they  supply,  and  neuralgic  pains  and  paresthesia  in  the  area  of  skin  to  which  they 
are  distributed :    no  oculopupillary  changes  are  to  be  found. 

The  thorax  is  frequently  found  to  be  altered  in  shape  in  certain  diseases. 

In  rickets,  the  ends  of  the  ribs,  where  they  join  the  costal  cartilages,  become  enlarged,  giving 
rise  to  the  so-called  "rickety  rosary,"  which  in  mild  cases  is  only  found  on  the  internal  surface 
of  the  thorax.  Lateral  to  these  enlargements  the  softened  ribs  sink  in,  so  as  to  present  a  groove 
passing  downward  and  lateralward  on  either  side  of  the  sternum.  This  bone  is  forced  forward 
by  the  bending  of  the  ribs,  and  the  antero-posterior  diameter  of  the  chest  is  increased.  The  ribs 
affected  are  the  second  to  the  eighth,  the  lower  ones  being  prevented  from  falling  in  by  the  pres- 
ence of  the  liver,  stomach,  and  spleen;  and  when  the  abdomen  is  distended,  as  it  often  is  in  rickets, 
the  lower  ribs  may  be  pushed  outward,  causing  a  transverse  groove  (Harrison's  sulcus)  just 
above  the  costal  arch.  This  deformity  or  forward  projection  of  the  sternum,  often  asymmetrical, 
is  known  as  pigeon  breast,  and  may  be  taken  as  evidence  of  active  or  old  rickets  except  in  cases 
of  primary  spinal  curvature.  In  many  instances  it  is  associated  in  children  with  obstruction  in 
the  upper  air  passages,  due  to  enlarged  tonsils  or  adenoid  growths.  In  some  rickety  children  or 
adults,  and  also  in  others  who  give  no  history  or  further  evidence  of  having  had  rickets,  an  opposite 
condition  obtains.  The  lower  part  of  the  sternum  and  often  the  xiphoid  process  as  well  are  deeply 
depressed  backward,  producing  an  oval  hollow  in  the  lower  sternal  and  upper  epigastric  regions. 
This  is  known  as  funnel  breast  (German,  Trichterbrust) ;  it  never  appears  to  produce  the  least 
disturbance  of  any  of  the  vital  functions.  The  phthisical  chest  is  often  long  and  narrow,  and  with 
great  obliquity  of  the  ribs  and  projection  of  the  scapula?.  In  pulmonary  emphysema  the  chest  is 
enlarged  in  all  its  diameters,  and  presents  on  section  an  almost  circular  outline.  It  has  received 
the  name  of  the  barrel-shaped  chest.  In  severe  cases  of  lateral  curvature  of  the  vertebral  column 
■  the  thorax  becomes  much  distorted.  In  consequence  of  the  rotation  of  the  bodies  of  the  vertebrae 
which  takes  place  in  this  disease,  the  ribs  opposite  the  convexity  of  the  dorsal  curve  become 
extremely  convex  behind,  being  thrown  out  and  bulging,  and  at  the  same  time  flattened  in  front, 
so  that  the  two  ends  of  the  same  rib  are  almost  parallel.  Coincidently  with  this  the  ribs  on  the 
opposite  side,  on  the  concavity  of  the  curve,  are  sunk  and  depressed  behind,  and  bulging  and 
convex  in  front. 

THE  SKULL. 

The  skull  is  supported  on  the  summit  of  the  vertebral  column,  and  is  of  an 
oval  shape,  wider  behind  than  in  front.  It  is  composed  of  a  series  of  flattened 
or  irregular  bones  which,  with  one  exception  (the  mandible),  are  immovably 
jointed  together.  It  is  divisible  into  two  parts:  (1)  the  cranium,  which  lodges 
and  protects  the  brain,  consists  of  eight  bones,  and  (2)  the  skeleton  of  the  face, 
of  fourteen,  as  follows : 


Cranium,  8  bones 


Occipital. 

Two  Parietals. 

Frontal. 

Two  Temporals. 

Sphenoidal. 

Ethmoidal. 

Skull,  22  bones   ]  ^  ^^.^  ^^^^^^ 

Two  Maxillae. 
Two  Lacrimals. 
Two  Zygomatics. 
Two  Palatines. 
Two  Inferior  Nasal  Conchse. 
Vomer. 
1^  Mandible. 

1  W.  Thorburn,  The  Medical  Chronicle,  Manchester,  1907,  4th  series,  xiv.  No.  3 


.  Face,  14  bones 


I 


THE  OCCIPITAL  BONE 


129 


In  the  Basle  nomenclature,  certain  bones  developed  in  association  with  the  nasal 
capsule,  viz.,  the  inferior  nasal  conchse,  the  lacrimals,  the  nasals,  and  the  vomer, 
are  grouped  as  cranial  and  not  as  facial  bones. 

The  hyoid  bone,  situated  at  the  root  of  the  tongue  and  attached  to  the  base 
of  the  skull  by  ligaments,  is  described  in  this  section. 


THE    CRANIAL   BONES    (OSSA    CRANE). 


The  Occipital  Bone  (Os  Occipitale). 


^H  The  occipital  bone  (Figs.  129,  130),  situated  at  the  back  and  lower  part  of  the 
cranium,  is  trapezoid  in  shape  and  curved  on  itself.  It  is  pierced  by  a  large  oval 
aperture,  the  foramen  magnum,  through  w^hich  the  cranial  cavity  communicates 
with  the  vertebral  canal. 


Constrictor  pharyngis 
superior 

Fig.   129. — Occipital  bone.     Outer  surface. 

The  curved,  expanded  plate  behind  the  foramen  magnum  is  named  the  squama; 
the  thick,  somewhat  quadrilateral  piece  in  front  of  the  foramen  is  called  the 
basilar  part,  whilst  on  either  side  of  the  foramen  is  the  lateral  portion. 

The  Squama  {squama  occipitalis). — ^The  squama,  situated  above  and  behind 
the  foramen  magnum,  is  curved  from  above  downward  and  from  side  to  side. 

Surfaces. — The  external  surface  is  convex  and  presents  midway  between  the 
summit  of  the  bone  and  the  foramen  magnum  a  prominence,  the  external  occipital 
protuberance.  Extending  lateralward  from  this  on  either  side  are  two  curved 
ines,  one  a  little  above  the  other.  The  upper,  often  faintly  marked,  is  named 
le  highest  nuchal  line,  and  to  it  the  galea  aponeurotica  is  attached.  The  lower 
9 


130 


OSTEOLOGY 


I 


is  termed  the  superior  nuchal  line.  That  part  of  the  squama  which  Hes  above 
the  highest  nuchal  lines  is  named  the  planum  occipitale,  and  is  covered  by  the 
Occipitalis  muscle;  that  below,  termed  the  planum  nuchale,  is  rough  and  irregular 
for  the  attachment  of  several  muscles.  From  the  external  occipital  protuberance 
a  ridge  or  crest,  the  median nuchalline,  often  faintly  marked,  descends  to  the  fora- 
men magnum,  and  affords  attachment  to  the  ligamentum  nuchae;  running  from 
the  middle  of  this  line  across  either  half  of  the  nuchal  plane  is  the  inferior  nuchal 
line.  Several  muscles  are  attached  to  the  outer  surface  of  the  squama,  thus: 
the  superior  nuchal  line  gives  origin  to  the  Occipitalis  and  Trapezius,  and  insertion 
to  the  Sternocleidomastoideus  and  Splenius  capitis:  into  the  surface  between 


Sufieri'of  Am. 


Fia. 


Inferior  A  ngle 
130. — Occipita  bone. 


Inner  surface. 


the  superior  and  inferior  nuchal  lines  the  Semispinalis  capitis  and  the  Obliquus 
capitis  superior  are  inserted,  while  the  inferior  nuchal  line  and  the  area  below 
it  receive  the  insertions  of  the  Recti  capitis  posteriores  major  and  minor.  The 
posterior  atlantooccipital  membrane  is  attached  around  the  postero-lateral  part 
of  the  foramen  magnum,  just  outside  the  margin  of  the  foramen. 

The  internal  surface  is  deeply  concave  and  divided  into  four  fossae  by  a  cruciate 
eminence.  The  upper  two  fossse  are  triangular  and  lodge  the  occipital  lobes  of 
the  cerebrum;  the  lower  two  are  quadrilateral  and  accommodate  the  hemispheres 
of  the  cerebellum.  At  the  point  of  intersection  of  the  four  divisions  of  the  cruciate 
eminence  is  the  internal  occipital  protuberance.  From  this  protuberance  the  upper 
division  of  the  cruciate  eminence  runs  to  the  superior  angle  of  the  bone,  and  on 


I 


THE  OCCIPITAL  BONE 


131 


^ 


one  side  of  it  (generally  the  right)  is  a  deep  groove,  the  sagittal  sulcus,  which  lodges 
the  hinder  part  of  the  superior  sagittal  sinus;  to  the  margins  of  this  sulcus  the  falx 
cerebri  is  attached.  The  lower  division  of  the  cruciate  eminence  is  prominent, 
and  is  named  the  internal  occipital  crest;  it  bifurcates  near  the  foramen  magnum 
and  gives  attachment  to  the  falx  cerebelli;  in  the  attached  margin  of  this  falx 
is  the  occipital  sinus,  which  is  sometimes  duplicated.  In  the  upper  part  of  the 
internal  occipital  crest,  a  small  depression  is  sometimes  distinguishable;  it  is 
termed  the  vermian  fossa  since  it  is  occupied  by  part  of  the  vermis  of  the  cerebellum. 
Transverse  grooves,  one  on  either  side,  extend  from  the  internal  occipital  protuber- 
ance to  the  lateral  angles  of  the  bone;  those  grooves  accommodate  the  transverse 
sinuses,  and  their  prominent  margins  give  attachment  to  the  tentorium  cerebelli. 
The  groove  on  the  right  side  is  usually  larger  than  that  on  the  left,  and  is 
continuous  with  that  for  the  superior  sagittal  sinus.  Exceptions  to  this  condition 
are,  however,  not  infrequent;  the  left  may  be  larger  than  the  right  or  the  two 
may  be  almost  equal  in  size.  The  angle  of  union  of  the  superior  sagittal  and  trans- 
verse sinuses  is  named  the  confluence  of  the  sinuses  {torcular  Herophili^),  and  its 
position  is  indicated  by  a  depression  situated  on  one  or  other  side  of  the 
protuberance. 

Lateral  Parts  (pars  lateralis). — The  lateral  parts  are  situated  at  the  sides  of 
the  foramen  magnum;  on  their  under  surfaces  are  the  condyles  for  articulation 
with  the  superior  facets  of  the  atlas.    The  condyles  are  oval  or  reniform  in  shape, 
and  their  anterior  extremities,  directed  forward  and  mediahvard,  are  closer  together 
than  their  posterior,  and  encroach  on  the  basilar  portion  of  the  bone;  the  posterior 
extremities  extend  back  to  the  level  of  the  middle  of  the  foramen  magnum.    The 
articular  surfaces  of  the  condyles  are  convex  from  before  backward  and  from 
side  to  side,  and  look  downward  and  lateralward.    To  their  margins  are  attached 
the  capsules  of  the  atlantooccipital  articulations,  and  on  the  medial  side  of  each 
is  a  rough  impression  or  tubercle  for  the  alar  ligament.     At  the  base  of  either 
condyle  the  bone  is  tunnelled  by  a  short  canal,  the  hypoglossal  canal  {anterior 
Icondyloid  foramen) .    This  begins  on  the  cranial  surface  of  the  bone  immediately 
[above  the  foramen  magnum,  and  is  directed  lateralward  and  forward  above  the 
j*condyle.    It  may  be  partially  or  completely  divided  into  two  by  a  spicule  of  bone ; 
it  gives  exit  to  the  hypoglossal  or  twelfth  cerebral  nerve,  and  entrance  to  a  meningeal 
branch  of  the  ascending  pharyngeal  artery.    Behind  either  condyle  is  a  depression, 
Ithe  condyloid  fossa,  which  receives  the  posterior  margin  of  the  superior  facet  of 
the  atlas  when  the  head  is  bent  backward;  the  floor  of  this  fossa  is  sometimes 
perforated  by  the  condyloid  canal,  through  which  an  emissary  vein  passes  from  the 
I  ttransverse  sinus.     Extending  lateralward  from  the  posterior  half  of  the  condyle 
lis  a  quadrilateral  plate  of  bone,  the  jugular  process,  excavated  in  front  by  the  jugvdar 
Ixiotch,  which,  in  the  articulated  skull,  forms  the  posterior  part  of  the  jugular  fora- 
men.   The  jugular  notch  may  be  divided  into  two  by  a  bony  spicule,  the  intra- 
jugular  process,  which  projects  lateralward  above  the  hypoglossal  canal.     The 
■under  surface  of  the  jugular  process  is  rough,  and  gives  attachment  to  the  Rectus 
•capitis  lateralis   muscle   and    the   lateral    atlantooccipital    ligament;    from  this 
surface  an  eminence,  the  paramastoid  process,  sometimes  projects  downward,  and 
may  be  of  sufficient  length  to  reach,  and  articulate  with,  the  transverse  process 
of  the  atlas.    Laterally  the  jugular  process  presents  a  rough  quadrilateral  or  tri- 

( angular  area  which  is  joined  to  the  jugular  surface  of  the  temporal  bone  by  a  plate 
of  cartilage;  after  the  age  of  twenty-five  this  plate  tends  to  ossify. 
The  upper  surface  of  the  lateral  part  presents  an  oval  eminence,  the  jugular 
tubercle,  which  overlies  the  hypoglossal  canal  and  is  sometimes  crossed  by  an 
oblique  groove  for  the  glossopharyngeal,  vagus,  and  accessory  nerves.     On  the 


'  The  columns  of  blood  coming  in  different  directions  were  supposed  to  be  pressed  together  at  this  point  (torcular, 
wine  press). 


132 


OSTEOLOGY 


upper  surface  of  the  jugular  process  is  a  deep  groove  which  curves  medial  ward 
and  forward  and  is  continuous  with  the  jugular  notch.  This  groove  lodges  the 
terminal  part  of  the  transverse  sinus,  and  opening  into  it,  close  to  its  medial 
margin,  is  the  orifice  of  the  condyloid  canal. 

Basilar  Part  (pars  hasilaris)  .■ — The  basilar  part  extends  forward  and  upward 
from  the  foramen  magnum,  and  presents  in  front  an  area  more  or  less  quadrilateral 
in  outline.  In  the  young  skull  this  area  is  rough  and  uneven,  and  is  joined  to  the 
body  of  the  sphenoid  by  a  plate  of  cartilage.  By  the  twenty-fifth  year  this  cartil- 
aginous plate  is  ossified,  and  the  occipital  and  sphenoid  form  a  continuous  bone. 
Surfaces. — On  its  lower  surface,  about  1  cm.  in  front  of  the  foramen  magnum, 
is  the  pharyngeal  tubercle  which  gives  attachment  to  the  fibrous  raphe  of  the  pharynx. 
On  either  side  of  the  middle  line  the  Longus  capitis  and  Rectus  capitis  anterior 
are  inserted,  and  immediately  in  front  of  the  foramen  magnum  the  anterior 
atlantooccipital  membrane  is  attached. 

The  upper  surface  presents  a  broad,  shallow  groove  which  inclines  upward 
and  forward  from  the  foramen  magnum;  it  supports  the  medulla  oblongata,  and 
near  the  margin  of  the  foramen  magnum  gives  attachment  to  the  membrana 
tectoria.  On  the  lateral  margins  of  this  surface  are  faint  grooves  for  the  inferior 
petrosal  sinuses. 

Foramen  Magnum. — The  foramen  magnum  is  a  large  oval  aperture  with  its  long 
diameter  antero-posterior;  it  is  wider  behind  than  in  front  where  it  is  encroached 
upon  by  the  condyles.  It  transmits  the  medulla  oblongata  and  its  membranes, 
the  accessory  nerves,  the  vertebral  arteries,  the  anterior  and  posterior  spinal 
arteries,  and  the  membrana  tectoria  and  alar  ligaments. 

Angles. — The  superior  angle  of  the  occipital  bone  articulates  with  the  occipital 
angles  of  the  parietal  bones  and,  in  the  fetal  skull,  corresponds  in  position  with  the 
posterior  fontanelle.  The  inferior  angle  is  fused  with  the  body  of  the  sphenoid. 
The  lateral  angles  are  situated  at  the  extremities  of  the  grooves  for  the  transverse 

sinuses:  each  is  received  into  the  interval 
between  the  mastoid  angle  of  the  parietal 
and  the  mastoid  part  of  the  temporal. 

Borders.  —  The  superior  borders  extend 
from  the  superior  to  the  lateral  angles: 
they  are  deeply  serrated  for  articulation 
with  the  occipital  borders  of  the  parietals, 
and  form  by  this  union  the  lambdoidal 
suture.  The  inferior  borders  extend  from 
the  lateral  angles  to  the  inferior  angle; 
the  upper  half  of  each  articulates  with 
the  mastoid  portion  of  the  corresponding 
temporal,  the  lower  half  with  the  petrous 
part  of  the  same  bone.  These  two  por- 
tions of  the  inferior  border  are  separated 
from  one  another  by  the  jugular  process, 
the  notch  on  the  anterior  surface  of  which 
forms  the  posterior  part  of  the  jugular 
foramen. 

Fio.   131. — Occipital  bone  at  birth. 

Structure. — The  occipital,  like  the  other  cranial 
bones,    consists  of  two   compact  lamellae,   called 
the  outer  and  inner  tables,  between  which  is  the  cancellous  tissue  or  diploe;  the  bone  is  especially- 
thick  at  the  ridges,  protuberances,  condyles,  and  anterior  part  of  the  basilar  part;  in  the  inferior 
fossse  it  is  thin,  semitransparent,  and  destitute  of  diploe. 

Ossification  (Fig.  131). — The  planum  occipitale  of  the  squama  is  developed  in  membrane, 
and  may  remam  separate  throughout  life  when  it  constitutes  the  interparietal  bone;  the  rest  of 


Planum 
occipitale 


Planum 

nv£hale 

Kerckring^s 
center 

Lateral 
part 


Basilar  part 


THE  PARIETAL  BONE 


133 


the  bone  is  developed  in  cartilage.  The  number  of  nuclei  for  the  planum  occipitale  is  usually- 
given  as  four,  two  appearing  near  the  middle  hne  about  the  second  month,  and  two  some  little 
distance  from  the  middle  line  about  the  third  month  of  fetal  life.  The  planum  nuchale  of  the 
scjuama  is  ossified  from  two  centers,  which  appear  about  the  seventh  week  of  fetal  Ufe  and  soon 
unite  to  form  a  single  piece.  Union  of  the  upper  and  lower  portions  of  the  squama  takes  place 
in  the  third  month  of  fetal  life.  An  occasional  center  (Kerckring)  appears  in  the  posterior  margin 
of  the  foramen  magnum  during  the  fifth  month;  this  forms  a  separate  ossicle  (sometimes  double) 
which  unites  with  the  rest  of  the  squama  before  birth.  Each  of  the  lateral  parts  begins  to 
ossify  from  a  single  center  during  the  eighth  week  of  fetal  Ufe.  The  basilar  portion  is  ossified 
from  two  centers,  one  in  front  of  the  other;  these  appear  about  the  sixth  week  of  fetal  life  and 
rapidly  coalesce.  Mall^  states  that  the  planum  occipitale  is  ossified  from  two  centers  and  the 
basilar  portion  from  one.  About  the  fourth  year  the  squama  and  the  two  lateral  portions  unite, 
and  about  the  sixth  year  the  bone  consists  of  a  single  piece.  Between  the  eighteenth  and  twenty- 
fifth  years  the  occipital  and  sphenoid  become  united,  forming  a  single  bone. 

Articulations. — The  occipital  articulates  with  six  bones :    the  two  parietals,  the  two  temporals, 
the  sphenoid,  and  the  atlas. 


The  Parietal  Bone  (Os  Parietale). 

The  parietal  bones  form,  by  their  union,  the  sides  and  roof  of  the  cranium.  Each 
bone  is  irregularly  quadrilateral  in  form,  and  has  two  surfaces,  four  borders, 
and  four  angles. 

Articulates  with  opposite  parietal  bone 


ticvlates 


rental 


Fig.    132. — Left  parietal  bone. 


With  mastoid  portion  of 
tetniDoral  bone 
Outer  surface. 


Surfaces. — The  external  surface  (Fig.  132)  is  convex,  smooth,  and  marked  near 
le  center  by  an  eminence,  the  parietal  eminence  (tuber  parietale),  which  indicates 
le  point  where  ossification  commenced.    Crossing  the  middle  of  the  bone  in  an 


•  American  Journal  of  Anatomy,  1906,  vol.  v. 


134 


OSTEOLOGY 


arched  direction  are  two  curved  lines,  the  superior  and  inferior  temporal  lines;  the 
former  gives  attachment  to  the  temporal  fascia,  and  the  latter  indicates  the  upper 
limit  of  the  muscular  origin  of  the  Temporalis.  Above  these  lines  the  bone  is 
covered  by  the  galea  aponeurotica;  below  them  it  forms  part  of  the  temporal 
fossa,  and  affords  attachment  to  the  Temporalis  muscle.  At  the  back  part  and 
close  to  the  upper  or  sagittal  border  is  the  parietal  foramen,  which  transmits  a 
vein  to  the  superior  sagittal  sinus,  and  sometimes  a  small  branch  of  the  occipital 
artery;  it  is  not  constantly  present,  and  its  size  varies  considerably. 

The  internal  surface  (Fig.  133)  is  concave;  it  presents  depressions  corresponding 
to  the  cerebral  convolutions,  and  numerous  furrows  for  the  ramifications  of  the 
middle  meningeal  vessel;^  the  latter  run  upward  and  backward  from  the  sphenoidal 
angle,  and  from  the  central  and  posterior  part  of  the  squamous  border.  Along 
the  upper  margin  is  a  shallow  groove,  which,  together  with  that  on  the  opposite 


Ul^^^^^^^'h. 


I 


Occipital 
angle 


Mastoid 
angle 


Frontal 
'   angle 


noidal  anple 


Fig.   133. — Left  parietal  bone.     Inner  surface. 


parietal,  forms  a  channel,  the  sagittal  sulcus,  for  the  superior  sagittal  sinus;  the 
edges  of  the  sulcus  afford  attachment  to  the  falx  cerebri.  Near  the  groove  are 
several  depressions,  best  marked  in  the  skulls  of  old  persons,  for  the  arachnoid 
granulations  {Pacchionian  bodies).  In  the  groove  is  the  internal  opening  of  the 
parietal  foramen  when  that  aperture  exists. 

Borders. — The  sagittal  border,  the  longest  and  thickest,  is  dentated  and  articu- 
lates with  its  fellow  of  the  opposite  side,  forming  the  sagittal  suture.  The  squamous 
border  is  divided  into  three  parts:  of  these,  the  anterior  is  thin  and  pointed,  bevelled 
at  the  expense  of  the  outer  surface,  and  overlapped  by  the  tip  of  the  great  wing 
of  the  sphenoid;  the  middle  portion  is  arched,  bevelled  at  the  expense  of  the  outer 
surface,  and  overlapped  by  the  squama  of  the  temporal ;  the  posterior  part  is  thick 
and  serrated  for  articulation  with  the  mastoid  portion  of  the  temporal.     The 

'  Journal  of  Anatomy  and  Physiology,  1912,  vol   xlvi 


I 


THE  FRONTAL  BONE  ^^^B  135 


IN 


frontal  border  is  deeply  serrated,  and  bevelled  at  the  expense  of  the  outer  surface 
above  and  of  the  inner  below;  it  articulates  with  the  frontal  bone,  forming  one- 
half  of  the  coronal  suture.  The  occipital  border,  deeph'  denticulated,  articulates 
with  the  occipital,  forming  one-half  of  the  lambdoidal  suture. 

Angles. — The  frontal  angle  is  practically  a  right  angle,  and  corresponds  with 
the  point  of  meeting  of  the  sagittal  and  coronal  sutures;  this  point  is  named  the 
bregma;  in  the  fetal  skull  and  for  about  a  year  and  a  half  after  birth  this  region  is 
membranous,  and  is  called  the  anterior  fontanelle.  The  sphenoidal  angle,  thin 
and  acute,  is  received  into  the  interval  between  the  frontal  bone  and  the  great 
wing  of  the  sphenoid.  Its  inner  surface  is  marked  by  a  deep  groove,  sometimes 
a  canal,  for  the  anterior  divisions  of  the  middle  meningeal  artery.  The  occipital 
angle  is  rounded  and  corresponds  with  the  point  of  meeting  of  the  sagittal  and 
lambdoidal  sutures — a  point  which  is  termed  the  lambda;  in  the  fetus  this  part 
of  the  skull  is  membranous,  and  is  called  the  posterior  fontanelle.  The  mastoid 
angle  is  truncated;  it  articulates  with  the  occipital  bone  and  with  the  mastoid 
portion  of  the  temporal,  and  presents  on  its  inner  surface  a  broad,  shallow  groove 
which  lodges  part  of  the  transverse  sinus.  The  point  of  meeting  of  this  angle 
ith  the  occipital  and  the  mastoid  part  of  the  temporal  is  named  the  asterion. 


Ossification. — The  parietal  bone  is  ossified  in  membrane  from  a  single  center,  which  appears 
t  the  parietal  eminence  about  the  eighth  week  of  fetal  life.     Ossification  gradually  extends  in 
n  radial  manner  from  the  center  toward  the  margins  of  the  bone;  the  angles  are  consequently 
he  parts  last  formed,  and  it  is  here  that  the  fontanelles  exist.    Occasionally  the  parietal  bone 
iS  divided  into  two  parts,  upper  and  lower,  by  an  antero-posterior  suture. 

Articulations. — The  parietal  articulates  with  five  bones:  the  opposite  parietal,  the  occipital, 
frontal,  temporal,  and  sphenoid. 

The  Frontal  Bone  (Os  Frontale). 

The  frontal  bone  resembles  a  cockle-shell  in  form,  and  consists  of  two  portions 
-a  vertical  portion,  the  squama,  corresponding  with  the  region  of  the  forehead; 
|fcnd  an  orbital  or  horizontal  portion,  which  enters  into  the  formation  of  the  roofs 
of  the  orbital  and  nasal  cavities. 

Squama  {squama  frontalis). — Surfaces. — The  external  surface  (Fig.  134)  of  this 
portion  is  convex  and  usually  exhibits,  in  the  lower  part  of  the  middle  line,  the 
remains  of  the  frontal  or  metopic  suture ;  in  infancy  this  suture  divides  the  bone  into 
I  two,  a  condition  which  may  persist  tlu-oughout  life.    On  either  side  of  this  suture, 
jiibout  3  cm.  above  the  supraorbital  margin,  is  a  rounded  elevation,  the  frontal  emi- 
I  iience  {tuber  frontale) .    These  eminences  vary  in  size  in  different  individuals,  are 
occasionally  unsymmetrical,.and  are  especially  prominent  in  young  skulls;  the  sur- 
iace  of  the  bone  above  them  is  smooth,  and  covered  by  the  galea  aponeurotica. 
teelow  the  frontal  eminences,  and  separated  from  them  by  a  shallow  groove,  are 
Itwo  arched  elevations,  the  superciliary  arches;  these  are  prominent  medially,  and 
fare  joined  to  one  another  by  a  smooth  elevation  named  the  glabella.    They  are 
larger  in  the  male  than  in  the  female,  and  their  degree  of  prominence  depends 
to  some  extent  on  the  size  of  the  frontal  air  sinuses;^  prominent  ridges  are,  how- 
ever, occasionally  associated  with  small  air  sinuses.     Beneath  each  superciliary 
arch  is  a  curved  and  prominent  margin,  the  supraorbital  margin,  which  forms  the 
upper  boundary  of  the  base  of  the  orbit,  and  separates  the  squama  from  the  orbital 
[portion  of  the  bone.     The  lateral  part  of  this  margin  is  sharp  and  prominent, 
laffording  to  the  eye,  in  that  situation,  considerable  protection  from  injury;  the 
Imedial  part  is  rounded.    At  the  junction  of  its  medial  and  intermediate  thirds  is 

1  Some  confusion  is  occasioned  to  students  commencing  the  study  of  anatomy  by  the  name  "sinus"  having  been 
•  given  to  two  different  kinds  of  space  connected  with  the  skull.  It  may  be  as  well,  therefore,  to  state  here  that  the 
"sinuses"  in  the  interior  of  the  cranium  which  produce  the  grooves  on  the  inner  surfaces  of  the  bones  are  venous 
channels  which  convey  the  blood  from  the  brain,  while  the  "sinuses"  external  to  the  cranial  cavity  (the  frontal, 
sphenoidal,  ethmoidal,  and  maxillary)  are  hollow  spaces  in  the  bones  themselves;  they  communicate  with  the  nasal 
savities  and  contain  air. 


■ 


136 


OSTEOLOGY 


a  notch,  sometimes  converted  into  a  foramen,  the  supraorbital  notch  or  foramen, 
which  transmits  the  supraorbital  vessels  and  nerve.  A  small  aperture  in  the  uppeT 
part  of  the  notch  transmits  a  vein  from  the  diploe  to  join  the  supraorbital  vein. 
The  supraorbital  margin  ends  laterally  in  the  zygomatic  process,  which  is  strong 
and  prominent,  and  articulates  with  the  zygomatic  bone.  Running  upward  and 
backward  from  this  process  is  a  well-marked  line,  the  temporal  line,  which  divid(!S 
into  the  upper  and  lower  temporal  lines,  continuous,  in  the  articulated  skull,  with 
the  corresponding  lines  on  the  parietal  bone.  The  area  below  and  behind  the  tem- 
poral line  forms  the  anterior  part  of  the  temporal  fossa,  and  gives  origin  to  the 
Temporalis  muscle.  Betw^een  the  supraorbital  margins  the  squama  projects  down- 
ward to  a  level  below  that  of  the  zygomatic  processes;  this  portion  is  known  as  the 
nasal  part  and  presents  a  rough,  uneven  interval,  the  nasal  notch,  which  articulates 


I 


Zygomatic 
process 


Frontal    i  spine 
Fig.   134. — Frontal  bone.     Outer  surface. 

on  either  side  of  the  middle  line  with  the  nasal  bone,  and  laterally  with  the  frontal 
process  of  the  maxilla  and  with  the  lacrimal.  The  term  nasion  is  applied  to  the 
middle  of  the  frontonasal  suture.  From  the  center  of  the  notch  the  nasal  process 
projects  downw^ard  and  forward  beneath  the  nasal  bones  and  frontal  processes  of 
the  maxilla^,  and  supports  the  bridge  of  the  nose.  The  nasal  process  ends  below 
in  a  sharp  spine,  and  on  either  side  of  this  is  a  small  grooved  surface  which  enters 
into  the  formation  of  the  roof  of  the  corresponding  nasal  cavity.  The  spine  forms 
part  of  the  septum  of  the  nose,  articulating  in  front  with  the  crest  of  the  nasal 
bones  and  behind  with  the  perpendicular  plate  of  the  ethmoid. 

The  internal  surface  (Fig.  135)  of  the  squama  is  concave  and  presents  in  the 
upper  part  of  the  middle  line  a  vertical  groove,  the  sagittal  sulcus,  the  edges  of 
which  unite  below  to  form  a  ridge,  the  frontal  crest;  the  sulcus  lodges  the  superior 
sagittal  sinus,  w'hile  its  margins  and  the  crest  afford  attachment  to  the  falx  cerebri. 


J 


THE  FRONTAL  BONE 


137 


The  crest  ends  below  in  a  small  notch  which  is  converted  into  a  foramen,  the  fora- 
men cecum,  by  articulation  with  the  ethmoid.  This  foramen  varies  in  size  in 
different  subjects,  and  is  frequently  impervious;  when  open,  it  transmits  a  vein 
from  the  nose  to  the  superior  sagittal  sinus.  On  either  side  of  the  middle  line  the 
bone  presents  depressions  for  the  convolutions  of  the  brain,  and  numerous  small 
furrows  for  the  anterior  branches  of  the  middle  meningeal  vessels.  Several  small, 
irregular  fossae  may  also  be  seen  on  either  side  of  the  sagittal  sulcus,  for  the 
reception  of  the  arachnoid  granulations. 

Orbital  or  Horizontal  Part  {yars  orbitalis). — This  portion  consists  of  two  thin 
triangular  plates,  the  orbital  plates,  which  form  the  vaults  of  the  orbits,  and  are 
separated  from  one  another  by  a  median  gap,  the  ethmoidal  notch. 


Supraorbital 
foramen 


With  maxilla 

With  nasal 


Frontal  sinus 


\vm  nasal,  •     i     \  jj,,^^^  surface  of  nasal  process 

With  ■perpendicular  plate  of  ethmoid       ||         forming  part  of  roof  of  nose 


* 


I 


Fig.   135. — Frontal  bone.     Inner  surface. 


Surfaces. — The  inferior  surface  (Fig.  135)  of  each  orbital  plate  is  smooth  and 
concave,  and  presents,  laterally,  under  cover  of  the  zygomatic  process,  a  shallow 
depression,  the  lacrimal  fossa,  for  the  lacrimal  gland;  near  the  nasal  part  is  a  depres- 
sion, the  fovea  trochlearis,  or  occasionally  a  small  trochlear  spine,  for  the  attach- 
ment of  the  cartilaginous  pulley  of  the  Obliquus  oculi  superior.  The  superior 
surface  is  convex,  and  marked  by  depressions  for  the  convolutions  of  the  frontal 

Llobes  of  the  brain,  and  faint  grooves  for  the  meningeal  branches  of  the  ethmoidal 

rvessels. 

The  ethmoidal  notch  separates  the  two  orbital  plates;  it  is  quadrilateral,  and 
filled,  in  the  articulated  skull,  by  the  cribriform  plate  of  the  ethmoid.  The  margins 
of  the  notch  present  several  half-cells  which,  when  united  with  corresponding 
half-cells  on  the  upper  surface  of  the  ethmoid,  complete  the  ethmoidal  air  cells. 
Two  grooves  cross  these  edges  transversely;  they  are  converted  into  the  anterior 


138 


OSTEOLOGY 


I 


and  posterior  ethmoidal  canals  by  the  ethmoid,  and  open  on  the  medial  wall  of  tlie 
orbit.  The  anterior  canal  transmits  the  nasociliary  nerve  and  anterior  ethmoidal 
vessels,  the  posterior,  the  posterior  ethmoidal  nerve  and  vessels.  In  front  of  tlie 
ethmoidal  notch,  on  either  side  of  the  frontal  spine,  are  the  openings  of  the  frontal 
air  sinuses.  These  are  two  irregular  cavities,  which  extend  backward,  upward, 
and  lateralward  for  a  variable  distance  between  the  two  tables  of  the  skull;  th<;y 
are  separated  from  one  another  by  a  thin  bony  septum,  which  often  deviates  to 
one  or  other  side,  with  the  result  that  the  sinuses  are  rarely  symmetrical.  Absent 
at  birth,  they  are  usually  fairly  well-developed  between  the  seventh  and  eighth 
years,  but  only  reach  their  full  size  after  puberty.  They  vary  in  size  in  different 
persons,  and  are  larger  in  men  than  in  women. ^  They  are  lined  by  mucous  mem- 
brane, and  each  communicates  with  the  corresponding  nasal  cavity  by  means  of  a 
passage  called  the  frontonasal  duct. 

Borders. — The  border  of  the  squama  is  thick,  strongly  serrated,  bevelled  at  the 
expense  of  the  inner  table  above,  where  it  rests  upon  the  parietal  bones,  and  at 
the  expense  of  the  outer  table  on  either  side,  where  it  receives  the  lateral  pressure 
of  those  bones;  this  border  is  continued  below  into  a  triangular,  rough  surface, 
which  articulates  with  the  great  wing  of  the  sphenoid.  The  posterior  borders  of 
the  orbital  plates  are  thin  and  serrated,  and  articulate  with  the  small  wings  of  the 
sphenoid. 

Structure. — The  squama  and  the  zygomatic  processes  are  very  thick,  consisting  of  diploic 
tissue  contained  between  two  compact  laminae;  the  diploic  tissue  is  absent  in  the  regions  occupied 
by  the  frontal  air  sinuses.  The  orbital  portion  is  thin,  translucent,  and  composed  entirely  of 
compact  bone;  hence  the  facility  with  which  instruments  can  penetrate  the  cranium  through 
this  part  of  the  orbit;  when  the  frontal  sinuses  are  exceptionally  large  they  may  extend  backward 
for  a  considerable  distance  into  the  orbital  portion,  which  in  such  cases  also  consists  of  onlj"^  two 
tables. 

Ossification  (Fig.  136).  —  The  frontal  bone  is  ossified  in  membrane  from  two  primary 
centers,  one  for  each  half,  which  appear  toward  the  end  of  the  second  month  of  fetal  life,  one 
above  each  supraorbital  margin.  From  each  of  these  centers  ossification  extends  upward  to  form 
the  corresponding  half  of  the  squama,  and  backward  to  form  the  orbital  plate.     The  spine  is 

ossified  from  a  pair  of  secondary  centers, 
«  on  either  side  of  the  middle  line;    similar 

*  centers  appear  in  the  nasal  part  and  zN'go- 

matic  processes.  At  birth  the  bone  consists 
of  two  pieces,  separated  by  the  frontal 
suture,  which  is  usually  obliterated,  except 
at  its  lower  part,  by  the  eighth  year,  but 
occasionally  persists  throughout  life.  It  is 
generally  maintained  that  the  development 
of  the  frontal  sinuses  begins  at  the  end  of 
the  first  or  beginning  of  the  second  year, 
but  Onodi's  researches  indicate  that  de- 
velopment begins  at  birth.  The  sinuses 
are  of  considerable  size  by  the  seventh  or 
eighth  year,  but  do  not  attain  their  full 
proportions  until  after  puberty. 

Articulations.  —  The  frontal  articulates 
with  twelve  bones:  the  sphenoid,  the  eth- 
moid, the  two  parietals,  the  two  nasals,  the 
two  maxillse,  the  two  lacrimals,  and  the 
two  zygomatics. 


Nasal  part 


Zygomatic  process 


Spine 
Fia.   136. — Frontal  bone  at  birth. 


The  Temporal  Bone  (Os  Temporale). 

The  temporal  bones  are  situated  at  the  sides  and  base  of  the  skull.  Each  consists 
of  five  parts,  viz.,  the  squama,  the  petrous,  mastoid,  and  tympanic  parts,  and  the 
styloid  process. 

•  Aldren  Turner  (The  Accessory  Sinuses  of  the  Nose,  1901)  gives  the  foljowirig  measurements  for  a  sinus  of  average 
size:  height,  \}/i  inches;  breadth,  1  inch;  depth  from  before  backward,  1  inch. 


THE  TEMPORAL  BONE 


139 


The  Squama  (squama  temporalis). — The  squama  forms  the  anterior  and  upper 
part  of  the  bone,  and  is  scale-like,  thin,  and  translucent. 

Surfaces.— Its  outer  surface  (P'ig.  137)  is  smooth  and  convex;  it  affords  attach- 
ment to  the  Temporalis  muscle,  and  forms  part  of  the  temporal  fossa;  on  its  hinder 
part  is  a  vertical  groove  for  the  middle  temporal  artery.  A  curved  line,  the  tem- 
poral line,  or  supramastoid  crest,  runs  backward  and  upward  across  its  posterior 
part;  it  serves  for  the  attachment  of  the  temporal  fascia,  and  limits  the  origin 
of  the  Temporalis  muscle.  The  boundary  between  the  squama  and  the  mastoid 
portion  of  the  bone,  as  indicated  by  traces  of  the  original  suture,  lies  about  1  cm. 
below  this  line.  Projecting  from  the  lower  part  of  the  squama  is  a  long,  arched 
process,  the  zygomatic  process.  This  process  is  at  first  directed  lateralward,  its 
two  surfaces  looking  upward  and  downward;  it  then  appears  as  if  twisted  inward 


Groove  for  middle 
temporal  artery 


Parietal  notch 

Swprameatal 
triangle 

Occipitalis 


Occipital  groove 
Tympanic  part 
Stylohyoideds 

Styloid  process 
Fig.  137. — Left  temporal  bone.     Outer  surface. 

ipon  itself,  and  runs  forward,  its  surfaces  now  looking  medial  ward  and  lateralward. 
?he  superior  border  is  long,  thin,  and  sharp,  and  serves  for  the  attachment  of  the 
_  smporal  fascia;  the  inferior,  short,  thick,  and  arched,  has  attached  to  it  some 
fibers  of  the  Masseter.  The  lateral  surface  is  convex  and  subcutaneous;  the  medial 
is  concave,  and  affords  attachment  to  the  Masseter.  The  anterior  end  is  deeply 
serrated  and  articulates  with  the  zygomatic  bone.    The  posterior  end  is  connected 

I  to  the  squama  by  two  roots,  the  anterior  and  posterior  roots.  The  posterior  root,  a 
prolongation  of  the  upper  border,  is  strongly  marked;  it  runs  backward  above  the 
External  acoustic  meatus,  and  is  continuous  with  the  temporal  line.  The  anterior 
root,  continuous  with  the  lower  border,  is  short  but  broad  and  strong;  it  is  directed 
medialward  and  ends  in  a  rounded  eminence,  the  articular  tubercle  (eminentia 
articidaris).     This  tubercle  forms  the  front  boundary  of  the  mandibular  fossa, 


h 


140 


OSTEOLOGY 


I 


and  in  the  fresh  state  is  covered  with  cartilage.  In  front  of  the  articular  tubenQe 
is  a  small  triangular  area  which  assists  in  forming  the  infratemporal  fossa;  this 
area  is  separated  from  the  outer  surface  of  the  squama  by  a  ridge  which  is  continu- 
ous behind  with  the  anterior  root  of  the  zygomatic  process,  and  in  front,  in  the 
articulated  skull,  with  the  infratemporal  crest  on  the  great  wing  of  the  sphenoid. 
Between  the  posterior  wall  of  the  external  acoustic  meatus  and  the  posterior  root 
of  the  zygomatic  process  is  the  area  called  the  suprameatal  triangle  (Macewen), 
or  mastoid  fossa,  through  which  an  instrument  may  be  pushed  into  the  tympanic 
antrum.  At  the  junction  of  the  anterior  root  with  the  zygomatic  process  is  a  pro- 
jection for  the  attachment  of  the  temporomandibular  ligament;  and  behind  the 
anterior  root'is  an  oval  depression,  forming  part  of  the  mandibular  fossa,  for  the 
reception  of  the  condyle  of  the  mandible.    The  mandibular  fossa  {glenoid  fossa) 


ctctl  ho9ie 


Eminentia 
arcuata 


Mastoid  foramen 

Aquceductus  vestihuli 

Aquceducttis  cochlcce 

Internal  acoustic  yneatua 
Fig.   138. — Left  temporal  bone.     Inner  surface. 

is  bounded,  in  front,  by  the  articular  tubercle;  behind,  by  the  tympanic  part  of 
the  bone,  which  separates  it  from  the  external  acoustic  meatus;  it  is  divided  into 
two  parts  by  a  narrow  slit,  the  petrotympanic  fissure  (Glaserian  fissure).  The 
anterior  part,  formed  by  the  squama,  is  smooth,  covered  in  the  fresh  state  with 
cartilage,  and  articulates  with  the  condyle  of  the  mandible.  Behind  this  part 
of  the  fossa  is  a  small  conical  eminence;  this  is  the  representative  of  a  prominent 
tubercle  which,  in  some  mammals,  descends  behind  the  condyle  of  the  mandible, 
and  prevents  its  backward  displacement.  The  posterior  part  of  the  mandibular 
fossa,  formed  by  the  tympanic  part  of  the  bone,  is  non-articular,  and  sometimes 
lodges  a  portion  of  the  parotid  gland.  The  petrotympanic  fissure  leads  into  the 
middle  ear  or  tympanic  cavity;  it  lodges  the  anterior  process  of  the  malleus,  and 
transmits  the  tympanic  branch  of  the  internal  maxillary  artery.     The  chorda 


i 


THE  TEMPORAL  BONE 


141 


tympani  nerve  passes  through  a  canal  (canal  of  Huguier),  separated  from  the  an- 
terior edge  of  the  petrotympanic  fissure  by  a  thin  scale  of  bone  and  situated  on 
the  lateral  side  of  the  auditory  tube,  in  the  retiring  angle  between  the  squama 
and  the  petrous  portion  of  the  temporal. 

The  internal  surface  of  the  squama  (Fig.  138)  is  concave;  it  presents  depressions 
corresponding  to  the  convolutions  of  the  temporal  lobe  of  the  brain,  and  grooves 
for  the  branches  of  the  middle  meningeal  vessels. 

Borders. — ^The  superior  border  is  thin,  and  bevelled  at  the  expense  of  the  internal 
table,  so  as  to  overlap  the  squamous,  border  of  the  parietal  bone,  forming  with 
it  the  squamosal  suture.  Posteriorly,  the  superior  border  forms  an  angle,  the 
parietal  notch,  with  the  mastoid  portion  of  the  bone.  The  antero-inferior  border 
is  thick,  serrated,  and  bevelled  at  the  expense  of  the  inner  table  above  and  of 
the  outer  below,  for  articulation  with  the  great  wing  of  the  sphenoid. 

Mastoid  Portion  {yars  mastoidea). — The  mastoid  portion  forms  the  posterior 
part  of  the  bone. 


Tympanic  antrum 

Tegmen  tympani 

Prominence,  of  lateral  semicircular  canal 
Prominence  of  facial  canal 
Fenestra  vestibuli 
Bristle  in  semicanal  for  Tensor  tympani 
Septum  canalis  muscviotubarii 

Bristle  m  hiatus  of  facial  canal 


Carotid  canal 
Bony  part  of  auditory  tube 
Promontory 
Bristle  in  pyramid 
Fenestra  cochleae 
Sulcus  tympanicus 
Mastoid  cells    ^''''^^  *^  stylomastoid  foramen 
Fia.  139. — Coronal  section  of  right  temporal  bone. 

Surfaces. — Its  outer  surface  (Fig.  137)  is  rough,  and  gives  attachment  to  the 
Occipitalis  and  Auricularis  posterior.  It  is  perforated  by  numerous  foramina;  one 
of  these,  of  large  size,  situated  near  the  posterior  border,  is  termed  the  mastoid 
foramen;  it  transmits  a  vein  to  the  transverse  sinus  and  a  small  branch  of  the  occipi- 
tal artery  to  the  dura  mater.  The  position  and  size  of  this  foramen  are  very 
■^variable;  it  is  not  always  present;  sometimes  it  is  situated  in  the  occipital  bone, 
pr  in  the  suture  between  the  temporal  and  the  occipital.  The  mastoid  portion  is 
continued  below  into  a  conical  projection,  the  mastoid  process,  the  size  and  form 
of  which  vary  somewhat;  it  is  larger  in  the  male  than  in  the  female.  This  process 
serves  for  the  attachment  of  the  Sternocleidomastoideus,  Splenius  capitis,  and 
Longissimus  capitis.  On  the  medial  side  of  the  process  is  a  deep  groove,  the 
astoid  notch  (digastric  fossa) ,  for  the  attachment  of  the  Digastricus;  medial  to 
is  is  a  shallow  furrow,  the  occipital  groove,  which  lodges  the  occipital  artery. 


OSTEOLOGY 


I 


The  inner  surface  of  the  mastoid  portion  presents  a  deep,  curved  groove,  the 
sigmoid  sulcus,  which  lodges  part  of  the  transverse  sinus;  in  it  may  be  seen  the 
opening  of  the  mastoid  foramen.  The  groove  for  the  transverse  sinus  is  separated 
from  the  innermost  of  the  mastoid  air  cells  by  a  very  thin  lamina  of  bone,  and  even 
this  may  be  partly  deficient. 

Borders. — The  superior  border  of  the  mastoid  portion  is  broad  and  serrated,  for 
articulation  with  the  mastoid  angle  of  the  parietal.  The  posterior  border,  also 
serrated,  articulates  with  the  inferior  border  of  the  occipital  between  the  lateral 
angle  and  jugular  process.  Anteriorly  the  mastoid  portion  is  fused  with  the 
descending  process  of  the  squama  above;  below  it  enters  into  the  formation  of 
the  external  acoustic  meatus  and  the  tympanic  cavity. 

A  section  of  the  mastoid  process  (Fig.  139)  shows  it  to  be  hollowed  out  into  a 
number  of  spaces,  the  mastoid  cells,  which  exhibit  the  greatest  possible  variety 
as  to  their  size  and  number.  At  the  upper  and  front  part  of  the  process  they  are 
large  and  irregular  and  contain  air,  but  toward  the  lower  part  they  diminish  in 
size,  while  those  at  the  apex  of  the  process  are  frequently  quite  small  and  contain 
marrow;  occasionally  they  are  entirely  absent,  and  the  mastoid  is  then  solid 
throughout.  In  addition  to  these  a  large  irregular  cavity  is  situated  at  the  upper 
and  front  part  of  the  bone.  It  is  called  the  tympanic  antrum,  and  must  be  distin- 
guished from  the  mastoid  cells,  though  it  communicates  with  them.  Like  the  mas- 
toid cells  it  is  filled  with  air  and  lined  by  a  prolongation  of  the  mucous  membrane 
of  the  tympanic  cavity,  with  which  it  communicates.  The  tympanic  antrum  is 
bounded  above  by  a  thin  plate  of  bone,  the  tegmen  tympani,  which  separates  it 
from  the  middle  fossa  of  the  base  of  the  skull;  below  by.  the  mastoid  process;  later- 
ally by  the  squama  just  below  the  temporal  line,  and  medially  by  the  lateral  semi- 
circular canal  of  the  internal  ear  which  projects  into  its  cavity.  It  opens  in  front 
into  that  portion  of  the  tympanic  cavity  which  is  known  as  the  attic  or  epitympanic 
recess.  The  tympanic  antrum  I's  a  cavity  of  some  considerable  size  at  the  time  of 
birth;  the  mastoid  air  cells  may  be  regarded  as  diverticula  from  the  antrum, 
and  begin  to  appear  at  or  before  birth;  by  the  fifth  year  they  are  well-marked, 
but  their  development  is  not  completed  until  toward  puberty. 

Petrous  Portion  {pars  petrosa  [pyramis]). — The  petrous  portion  or  pyramid  is 
pyramidal  and  is  wedged  in  at  the  base  of  the  skull  between  the  sphenoid  and 
occipital.  Directed  medialward,  forward,  and  a  little  upward,  it  presents  for 
examination  a  base,  an  apex,  three  surfaces,  and  three  angles,  and  contains,  in 
its  interior,  the  essential  parts  of  the  organ  of  hearing. 

Base. — The  base  is  fused  with  the  internal  surfaces  of  the  squama  and  mastoid 
portion. 

Apex. — ^The  apex,  rough  and  uneven,  is  received  into  the  angular  interval  between 
the  posterior  border  of  the  great  wing  of  the  sphenoid  and  the  basilar  part  of  the 
occipital;  it  presents  the  anterior  or  internal  orifice  of  the  carotid  canal,  and 
forms  the  postero-lateral  boundary  of  the  foramen  lacerum. 

Surfaces. — ^The  anterior  surface  forms  the  posterior  part  of  the  middle  fossa  of 
the  base  of  the  skull,  and  is  continuous  with  the  inner  surface  of  the  squamous 
portion,  to  which  it  is  united  by  the  petrosquamous  suture,  remains  of  which  are 
distinct  even  at  a  late  period  of  life.  It  is  marked  by  depressions  for  the  convolu- 
tions of  the  brain,  and  presents  six  points  for  examination:  (1)  near  the  center, 
an  eminence  (eminentia  arcuata)  which  indicates  the  situation  of  the  superior  semi- 
circular canal;  (2)  in  front  of  and  a  little  lateral  to  this  eminence,  a  depression  indi- 
cating the  position  of  the  tympanic  cavity :  here  the  layer  of  bone  which  separates 
the  tympanic  from  the  cranial  cavity  is  extremely  thin,  and  is  known  as  the 
tegmen  tympani;  (3)  a  shallow  groove,  sometimes  double,  leading  lateralward  and 
backward  to  an  oblique  opening,  the  hiatus  of  the  facial  canal,  for  the  passage  of 
the  greater  superficial  petrosal  nerve  and  the  petrosal  branch  of  the  middle  men- 


I 


THE  TEMPORAL  BONE 


143 


ingeal  artery;  (4)  lateral  to  the  hiatus,  a  smaller  opening,  occasionally  seen,  for 
the  passage  of  the  lesser  superficial  petrosal  nerve;  (5)  near  the  apex  of  the  bone, 
the  termination  of  the  carotid  canal,  the  wall  of  which  in  this  situation  is  deficient 
in  front;  (6)  above  this  canal  the  shallow  trigeminal  impression  for  the  reception 
of  the  semilunar  ganglion. 

The  posterior  surface  (Fig.  138)  forms  the  front  part  of  the  posterior  fossa  of 
the  base  of  the  skull,  and  is  continuous  with  the  inner  surface  of  the  mastoid 
portion.  Near  the  center  is  a  large  orifice,  the  internal  acoustic  meatus,  the  size  of 
which  varies  considerably;  its  margins  are  smooth  and  rounded,  and  it  leads  into 
a  short  canal,  about  1  cm.  in  length,  which  runs  lateralward.  It  transmits  the 
facial  and  acoustic  nerves  and  the  internal  auditory  branch  of  the  basilar  artery. 
The  lateral  end  of  the  canal  is  closed  by  a  vertical  plate,  which  is  divided  by  a 
horizontal  crest,  the  crista  falciformis,  into  two  unequal  portions  (Fig.  140).  Each 
I)ortion  is  further  subdivided  by  a  vertical  ridge  into  an  anterior  and  a  posterior 
])art.  In  the  portion  beneath  the  crista  falciformis  are  three  sets  of  foramina; 
one  group,  just  below  the  posterior  part  of 
the  crest,  situated  in  the  area  cribrosa  media, 
consists  of  several  small  openings  for  the 
nerves  to  the  saccule;  below  and  behind  this 
iirea  is  the  foramen  singulare,  or  opening  for 
the  nerve  to  the  posterior  semicircular  duct; 
in  front  of  and  below  the  first  is  the  tractus 
spiralis  foraminosus,  consisting  of  a  number  of 
small  spirally  arranged  openings,  which  encircle 
the  canalis  centralis  cochleae;  these  openings 
together  with  this  central  canal  transmit  the 
nerves  to  the  cochlea.  The  portion  above 
the  crista  falciformis  presents  behind,  the 
area  cribrosa  superior,  pierced  by  a  series  of 
small  openings,  for  the  passage  of  the  nerves 
to  the  utricle  and  the  superior  and  lateral 
semicircular  ducts,  and,  in  front,  the  area 
facialis,  with  one  large  opening,  the  com- 
mencement of  the  canal  for  the  facial  nerve 
(aquaeductus  Fallopii).  Behind  the  internal 
acoustic  meatus  is  a  small  slit  almost  hidden 
by  a  thin  plate  of  bone,  leading  to  a  canal, 
the  aquaeductus  vestibuli,  which  transmits  the 

ductus  endolymphaticus  together  with  a  small  artery  and  vein.  Above  and 
between  these  two  openings  is  an  irregular  depression  which  lodges  a  process  of 
the  dura  mater  and  transmits  a  small  vein;  in  the  infant  this  depression  is  repre- 
sented by  a  large  fossa,  the  subarcuate  fossa,  which  extends  backward  as  a  blind 
jtunnel  under  the  superior  semicircular  canal. 

'"  The  inferior  surface  (Fig.  141)  is  rough  and  irregular,  and  forms  part  of  the 
exterior  f>i  the  base  of  the  skull.  It  presents  eleven  points  for  examination:  (1) 
near  the  apex  is  a  rough  surface,  quadrilateral  in  form,  which  serves  partly  for  the 
attachment  of  the  Levator  veli  palatini  and  the  cartilaginous  portion  of  the  audi- 
tory tube,  and  partly  for  connection  with  the  basilar  part  of  the  occipital  bone 
through  the  intervention  of  some  dense  fibrous  tissue;  (2)  behind  this  is  the  large 
circular  aperture  of  the  carotid  canal,  which  ascends  at  first  vertically,  and  then, 
making  a  bend,  runs  horizontally  forward  and  medialward;  it  transmits  into  the 
cranium  the  internal  carotid  artery,  and  the  carotid  plexus  of  nerves;  (3)  medial 
to  the  opening  for  the  carotid  canal  and  close  to  its  posterior  border,  in  front  of  the 
jugular  fossa,  is  a  triangular  depression;  at  the  apex  of  this  is  a  small  opening,  the 


Fig.  140. — Diagrammatic  view  of  the  fundus 
of  the  right  internal  acoustic  meatus.  (Testut.) 
1.  Crista  falciformis.  2.  Area  facialis,  with  (2') 
internal  opening  of  the  facial  canal.  3.  Ridge 
separating  the  area  facialis  from  the  area  crib- 
rosa superior.  4.  Area  cribrosa  superior,  with 
(4')  openings  for  nerve  filaments.  5.  Anterior 
inferior  cribriform  area,  with  (5')  the  tractus 
spiralis  foraminosus,  and  (5")  the  canalis  cen- 
tralis of  the  cochlea.  6.  Ridge  separating  the 
tractus  spiralis  foraminosus  from  the  area  crib- 
rosa media.  7.  Area  cribrosa  media,  with  (7') 
orifices  for  nerves  to  saccule.  8.  Foramen 
singulare. 


II 


144 


OSTEOLOGY 


I 


aquaeductus  cochleae,  which  lodges  a  tubular  prolongation  of  the  dura  mater  establish- 
ing a  communication  between  the  perihinphatic  space  and  the  subarachnoid  space, 
and  transmits  a  vein  from  the  cochlea  to  join  the  internal  jugular;  (4)  behind  these 
openings  is  a  deep  depression,  the  jugular  fossa,  of  variable  depth  and  size  in  different 
skulls;  it  lodges  the  bulb  of  the  internal  jugular  vein;  (5)  in  the  bony  ridge  dividing 
the  carotid  canal  from  the  jugular  fossa  is  the  small  inferior  tympanic  canaliculus 
for  the  passage  of  the  tympanic  branch  of  the  glossopharyngeal  nerve;  (6)  in  the 
lateral  part  of  the  jugular  fossa  is  the  mastoid  canaliculus  for  the  entrance  of  the 
auricular  branch  of  the  vagus  nerve;  (7)  behind  the  jugular  fossa  is  a  quadrilateral 
area,  the  jugular  surface,  covered  with  cartilage  in  the  fresh  state,  and  articulating 
with  the  jugular  process  of  the  occipital  bone;  (8)  extending  backward  from  the 
carotid  canal  is  the  vaginal  process,  a  sheath-like  plate  of  bone,  which  divides 

Semicanals  for 

auditory 

tube  a  lid 

Tensor 

tympani 


StylopJiaryngeua 


Lev.  vdi  palatini 

Rough  quadrilaieral  surface 

Openiitg  of  carotid  canal 

Inferior  tympanic  canaliculus 

Aquceductiis  cochlew 

Mastoid  canalicvlus 

Jugular  fossa 

Vaginal  process 

Styloid  process 

Stylomastoid  foramen 

J^igUlar  surface 

Tympanomastoid  fissure 


Fia.  141. — Left  temporal  bone.     Inferior  surface. 

behind  into  two  laminae;  the  lateral  lamina  is  continuous  with  the  tympanic  part 
of  the  bone,  the  medial  with  the  lateral  margin  of  the  jugular  surface;  (9)  between 
these  laminae  is  the  styloid  process,  a  sharp  spine,  about  2.5  cm.  in  length;  (10) 
between  the  styloid  and  mastoid  processes  is  the  stylomastoid  foramen;  it  is  the 
termination  of  the  facial  canal,  and  transmits  the  facial  nerve  and  stylomastoid 
artery;  (11)  situated  between  the  tympanic  portion  and  the  mastoid  process  is  the 
tympanomastoid  fissure,  for  the  exit  of  the  auricular  branch  of  the  vagus  nerve. 
Angles. — ^The  superior  angle,  the  longest,  is  grooved  for  the  superior  petrosal 
sinus,  and  gives  attachment  to  the  tentorium  cerebelli;  at  its  medial  extremity 
is  a  notch,  in  which  the  trigeminal  nerve  lies.  The  posterior  angle  is  intermediate 
in  length  between  the  superior  and  the  anterior.  Its  medial  half  is  marked  by 
a  sulcus,  which  forms,  with  a  corresponding  sulcus  on  the  occipital  bone,  the 
channel  for  the  inferior  petrosal  sinus.  Its  lateral  half  presents  an  excavation 
— the  jugular  fossa — which,  with  the  jugular  notch  on  the  occipital,  forms  the 


THE  TEMPORAL  BONE 


145 


t 


jugular  foramen ;  an  eminence  occasionally  projects  from  the  center  of  the  fossa, 
and  divides  the  foramen  into  two.  The  anterior  angle  is  divided  into  two  parts 
— a  lateral  joined  to  the  squama  by  a  suture  (petrosquamous),  the  remains  of  which 
are  more  or  less  distinct;  a  medial,  free,  which  articulates  with  the  spinous  process 
of  the  sphenoid. 

At  the  angle  of  junction  of  the  petrous  part  and  the  squama  are  two  canals, 
one  above  the  other,  and  separated  by  a  thin  plate  of  bone,  the  septum  canalis 
musculotubarii  {processus  cochleariformis) ;  both  canals  lead  into  the  tympanic 
cavity.  The  upper  one  (semicanalis  m.  tensoris  tympani)  transmits  the  Tensor 
tympani,  the  lower  one  (semicanalis  tubcB  auditivw)  forms  the  bony  part  of  the 
auditory  tube. 

The  tympanic  cavity,  auditory  ossicles,  and  internal  ear,  are  described  with 
the  organ  of  hearing. 

Tympanic  Part  (jmrs  tympanica). — The  tympanic  part  is  a  curved  plate  of  bone 
lying  below  the  squama  and  in  front  of  the  mastoid  process. 

Surfaces. — Its  postero-superior  surface  is  concave,  and  forms  the  anterior  wall, 
the  floor,  and  part  of  the  posterior  wall  of  the  bony  external  acoustic  meatus. 
]Medially,  it  presents  a  narrow  furrow,  the  tympanic  sulcus,  for  the  attachment 
of  the  tympanic  membrane.  Its  antero-inferior  surface  is  quadrilateral  and  slightly 
concave;  it  constitutes  the  posterior  boundary  of  the  mandibular  fossa,  and  is 
in  contact  w^ith  the  retromandibular  part  of  the  parotid  gland. 

Borders. — Its  lateral  border  is  free  and  rough,  and  gives  attachment  to  the  car- 
tilaginous part  of  the  external  acoustic  meatus.  Internally,  the  tympanic  part 
is  fused  with  the  petrous  portion,  and  appears  in  the  retreating  angle  between 
it  and  the  squama,  where  it  lies  below  and  lateral  to  the  orifice  of  the  auditory 
tube.  Posteriorly,  it  blends  with  the  squama  and  mastoid  part,  and  forms  the 
anterior  boundary  of  the  tympanomastoid  fissure.  Its  upper  border  fuses  laterally 
with  the  back  of  the  postglenoid  process,  w^hile  medially  it  bounds  the  petro- 
tympanic fissure.  The  medial  part  of  the  lower  border  is  thin  and  sharp;  its  lateral 
part  splits  to  enclose  the  root  of  the  styloid  process,  and  is  therefore  named  the 
vaginal  process.  The  central  portion  of  the  tympanic  part  is  thin,  and  in  a  consid- 
I  arable  percentage  of  skulls  is  perforated  by  a  hole,  the  foramen  of  Huschke. 

The  external  acoustic  meatus  is  nearly  2  cm.  long  and  is  directed  inward  and 
slightly  forward:  at  the  same  time  it  forms  a  slight  curve,  so  that  the  floor  of  the 
canal  is  convex  upward.  In  sagittal  section  it  presents  an  oval  or  elliptical  shape 
•  with  the  long  axis  directed  downward  and  slightly  backward.  Its  anterior  wall 
land  floor  and  the  lower  part  of  its  posterior  wall  are  formed  by  the  tympanic 
part;  the  roof  and  upper  part  of  the  posterior  wall  by  the  squama.  Its  inner 
end  is  closed,  in  the  recent  state,  by  the  tympanic  membrane;  the  upper  limit 
of  its  outer  orifice  is  formed  by  the  posterior  root  of  the  zygomatic  process,  imme- 
diately below  which  there  is  sometimes  seen  a  small  spine,  the  suprameatal  spine, 
situated  at  the  upper  and  posterior  part  of  the  orifice. 

Styloid  Process  {processus  styloideus) . — The  styloid  process  is  slender,  pointed, 
and  of  varying  length;  it  projects  downward  and  forw^ard,  from  the  under  surface 
■  of  the  temporal  bone.  Its  proximal  part  (tympanohyal)  is  ensheathed  by  the 
'vaginal  process  of  the  tympanic  portion,  while  its  distal  part  (stylohyal)  gives 
attachment  to  the  stylohyoid  and  stylomandibular  ligaments,  and  to  the  Stylo- 
glossus, Stylohyoideus,  and  Stylopharyngeus  muscles.  The  stylohyoid  ligament 
extends  from  the  apex  of  the  process  to  the  lesser  cornu  of  the  hyoid  bone,  and 
in  some  instances  is  partially,  in  others  completely,  ossified. 

Structure. — The  structure  of  the  squama  is  like  that  of  the  other  cranial  bones:  the  mastoid 
portion  is  spongy,  and  the  petrous  portion  dense  and  hard. 

Ossification. — The  temporal  bone  is  ossified  from  eight  centers,  exclusive  of  those  for  the  internal 
ear  and  the  tympanic  ossicles,  viz.,  one  for  the  squama  including  the  zygomatic  process,  one  for 


k 


10 


146 


OSTEOLOGY 


I 


the  tympanic  part,  four  for  the  petrous  and  mastoid  parts,  and  two  for  the  styloid  process.  Just 
before  the  close  of  fetal  Hfe  (Fig.  142)  the  temporal  bone  consists  of  three  principal  parts:  1. 
The  squama  is  ossified  in  membrane  from  a  single  nucleus,  which  appears  near  the  root  of  tlie 
zygomatic  process  about  the  second  month.  2.  The  petromastoid  part  is  developed  from  four 
centers,  which  make  their  appearance  in  the  cartilaginous  ear  capsule  about  the  fifth  or  sixth 
month.  One  (prootic)  appears  in  the  neighborhood  of  the  eminentia  arcuata,  spreads  in  front 
and  above  the  internal  acoustic  meatus  and  extends  to  the  apex  of  the  bone;  it  forms  part  of  the 


Septum  canalis  musculotvbarii 

Fenestra  vestibuli 
Tympanic  antrum. 


Sulcus  tym,panicus 


Bristle  in  facial 
canal 


Lateral  wall  of 
tympanic  antrum 


Fig.   142. 


-The  three  principal  parts  of  the  tempora  bone  at  birth.     1.  Outer  surface  of  petromastoid  part. 
2.   Outer  surface  of  tympanic  ring.     3.   Inner  surface  of  squama. 


cochlea,  vestibule,  superior  semicircular  canal,  and  medial  wall  of  the  tympanic  cavity.  A  second 
(opisthotic)  appears  at  the  promontory  on  the  medial  wall  of  the  tympanic  cavity  and  surrounds 
the  fenestra  cochlea?;  it  forms  the  floor  of  the  tympanic  cavity  and  vestibule,  surrounds  the  carotid 
canal,  invests  the  lateral  and  lower  part  of  the  cochlea,  and  spreads  medially  below  the  internal 
acoustic  meatus.    A  third  (pterotic)  roofs  in  the  tympanic  cavity  and  antrum;  while  the  fourth 


Squ/ima 


Squama 


Petrosquamous 
suiure 


Petrosquamous  suture 
Eminentia  arcuaia 


Tympanic  ring 


Petromastoid  portion 


Fig. 


143. — Temporal  bone  at  birth. 
Outer  aspect. 


Fossa  suharcuata 

Internal  acoustic  meatus 

Fig.   144. — Temporal  bone  at  birth.     Inner 
aspect. 


(epiotic)  appears  near  the  posterior  semicircular  canal  and  extends  to  form  the  mastoid  process 
(Vrolik).  3.  The  tympanic  ring  is  an  incomplete  circle,  in  the  concavity  of  which  is  a  groove, 
the  tympanic  sulcus,  for  the  attachment  of  the  circumference  of  the  tympanic  membrane.  This 
ring  expands  to  form  the  tympanic  part,  and  is  ossified  in  membrane  from  a  single  center  which 
appears  about  the  third  month.  The  styloid  process  is  developed  from  the  proximal  part  of  the 
cartilage  of  the  second  branchial  or  hyoid  arch  by  two  centers:  one  for  the  proximal  part,  the 
iympanohyal,  appears  before  birth;  the  other,  comprising  the  rest  of  the  process,  is  named  the 


J 


THE  SPHENOID  BONE  HHP  147 


I 


I 


stylohyal,  and  does  not  appear  until  after  birth.  The  tympanic  ring  unites  with  the  squama 
shortly  before  birth;  the  petromastoid  part  and  squama  join  during  the  first  year,  and  the  tym- 
panohyal  portion  of  the  styloid  process  about  the  same  time  (Figs.  143,  144).  The  stylohyal 
does  not  unite  with  the  rest  of  the  bone  until  after  puberty,  and  in  some  skulls  never  at  all. 

The  chief  subsequent  changes  in  the  temporal  bone  apart  from  increase  in  size  are:  (1)  The 
tympanic  ring  extends  outward  and  backward  to  form  the  tympanic  part.  This  extension  does 
not,  however,  take  place  at  an  equal  rate  all  around  the  circumference  of  the  ring,  but  occurs  most 
rapidly  on  its  anterior  and  posterior  portions,  and  these  outgrowths  meet  and  blend,  and  thus, 
for  a  time,  there  exists  in  the  floor  of  the  meatus  a  foramen,  the  foramen  of  Huschke;  this  foramen 
is  usually  closed  about  the  fifth  year,  but  may  persist  throughout  life.  (2)  The  mandibular  fossa 
is  at  first  extremely  shallow,  and  looks  lateralward  as  well  as  downward;  it  becomes  deeper  and 
is  ultimately  directed  downward.  Its  change  in  direction  is  accounted  for  as  follows.  The  part 
of  the  squama  which  forms  the  fossa  lies  at  first  below  the  level  of  the  zygomatic  process.  As, 
however,  the  base  of  the  skull  increases  in  width,  this  lower  part  of  the  squama  is  directed  hori- 
zontally inward  to  contribute  to  the  middle  fossa  of  the  skull,  and  its  surfaces  therefore  come 
to  look  upward  and  downward;  the  attached  portion  of  the  zygomatic  process  also  becomes 
everted,  and  projects  like  a  shelf  at  right  angles  to  the  squama.  (3)  The  mastoid  portion  is  at 
first  quite  flat,  and  the  stylomastoid  foramen  and  rudimentary  styloid  process  lie  immediately 
behind  the  tympanic  ring.  With  the  development  of  the  air  cells  the  outer  part  of  the  mastoid 
portion  grows  downward  and  forward  to  form  the  mastoid  process,  and  the  styloid  process  and 
stylomastoid  foramen  now  come  to  lie  on  the  under  surface.  The  descent  of  the  foramen  is 
necessarily  accompanied  by  a  corresponding  lengthening  of  the  facial  canal.  (4)  The  downward 
and  forward  growth  of  the  mastoid  process  also  pushes  forward  the  tympanic  part,  so  that  the 
portion  of  it  which  formed  the  original  floor  of  the  meatus  and  contained  the  foramen  of  Huschke 
is  ultimately  found  in  the  anterior  wall.  (5)  The  fossa  subarcuata  becomes  filled  up  and  almost 
obliterated. 

Articulations. — The  temporal  articulates  with  five  bones :  occipital,  parietal,  sphenoid,  mandible 
and  zygomatic. 

I  The  Sphenoid  Bone  (Os  Sphenoidale). 

The  sphenoid  bone  is  situated  at  the  base  of  the  skull  in  front  of  the  temporals 
and  basilar  part  of  the  occipital.  It  somewhat  resembles  a  bat  with  its  wings 
extended,  and  is  divided  into  a  median  portion  or  body,  two  great  and  two  small 
wings  extending  outward  from  the  sides  of  the  body,  and  two  pterygoid  processes 
which  project  from  it  below\ 

[  Body  {corpus  syhenoidale) . — The  body,  more  or  less  cubical  in  shape,  is  hollowed 
out  in  its  interior  to  form  two  large  cavities,  the  sphenoidal  air  sinuses,  which  are 
separated  from  each  other  by  a  septum. 

Surfaces. — The  superior  surface  of  the  body  (Fig.  145)  presents  in  front  a  promi- 
ent  spine,  the  ethmoidal  spine,  for  articulation  with  the  cribriform  plate  of  the 
ithmoid;  behind  this  is  a  smooth  surface  slightly  raised  in  the  middle  line,  and 
grooved  on  either  side  for  the  olfactory  lobes  of  the  brain.  This  surface  is  bounded 
behind  by  a  ridge,  which  forms  the  anterior  border  of  a  narrow,  transverse  groove, 
the  chiasmatic  groove  {optic  groove),  above  and  behind  which  lies  the  optic  chiasma; 
Ihe  groove  ends  on  either  side  in  the  optic  foramen,  which  transmits  the  optic 
nerve  and  ophthalmic  artery  into  the  orbital  cavity.  Behind  the  chiasmatic 
groove  is  an  elevation,  the  tuberculum  sellae;  and  still  more  posteriorly,  a  deep 
depression,  the  sella  tiu'cica,  the  deepest  part  of  which  lodges  the  hypophysis 
cerebri  and  is  known  as  the  fossa  hypophyseos.  The  anterior  boundary  of  the 
sella  turcica  is  completed  by  two  small  eminences,  one  on  either  side,  called  the 
middle  clinoid  processes,  while  the  posterior  boundary  is  formed  by  a  square- 
shaped  plate  of  bone,  the  dorsum  sellae,  ending  at  its  superior  angles  in  two  tubercles, 
the  posterior  clinoid  processes,  the  size  and  form  of  which  vary  considerably  in 
different  individuals.  The  posterior  clinoid  processes  deepen  the  sella  turcica, 
and  give  attachment  to  the  tentorium  cerebelli.  On  either  side  of  the  dorsum 
sellse  is  a  notch  for  the  passage  of  the  abducent  nerve,  and  below  the  notch  a  sharp 
process,  the  petrosal  process,  which  articulates  with  the  apex  of  the  petrous  portion 
of  the  temporal  bone,  and  forms  the  medial  boundary  of  the  foramen  lacerum. 


148 


OSTEOLOGY 


I 


Behind  the  dorsum  sellse  is  a  shallow  depression,  the  clivus,  which  slopes  obliquely 
backward,  and  is  continuous  with  the  groove  on  the  basilar  portion  of  the  occipii:al 
bone;  it  supports  the  upper  part  of  the  pons. 


Middle  Clinoid  j)rocess 
Posterim-  Clinoid  process 


Ethmoidal 
spine 

Groove  for 
olfactorji 
lobe 


Optic  foramen 
Superior  orbital 
fissure 

Forainen  rotundum 

Foramen  Vesalii 

Foramen  ovale 

Foramen  spinosum 


Spina  angularis 


With 
jialatine 


Fig.  145. — Sphenoid  bone.     Upper  surface. 


The  lateral  surfaces  of  the  body  are  united  with  the  great  w  ings  and  the  medial 
pterygoid  plates.  Above  the  attachment  of  each  great  wing  is  a  broad  groove, 
curved  something  like  the  italic  letter  /;  it  lodges  the  internal  carotid  artery  and 
the  cavernous  sinus,  and  is  named  the  carotid  groove.     Along  the  posterior  part 


Tensor  vel 
palatini 


Medial  pteryijoid  plat, 
Hamiilu. 

Fig.   146. — Sphenoid  bone.     Anterior  and  inferior  surfaces. 

of  the  lateral  margin  of  this  groove,  in  the  angle  between  the  body  and  great  wing, 
is  a  ridge  of  bone,  called  the  lingula. 

The  posterior  surface,  quadrilateral  in  form  (I'ig.  147),  is  joined,  during  infancy 
and  adolescence,  to  the  basilar  part  of  the  occipital  bone  by  a  plate  of  cartilage. 


THE  SPHENOID  BONE 


149 


Between  the  eighteenth  and  twenty-fifth  years  this  becomes  ossified,  ossification 
commencing  above  and  extending  downward. 

The  anterior  surface  of  the  body  (Fig.  146)  presents,  in  the  middle  line,  a  vertical 
crest,  the  sphenoidal  crest,  which  articulates  with  the  perpendicular  plate  of  the 
ethmoid,  and  forms  part  of  the  septum  of  the  nose.  On  either  side  of  the  crest 
is  an  irregular  opening  leading  into  the  corresponding  sphenoidal  air  sinus.  These 
sinuses  are  two  large,  irregular  cavities  hollowed  out  of  the  interior  of  the  body 
of  the  bone,  and  separated  from  one  another  by  a  bony  septum,  which  is  commonly 
bent  to  one  or  the  other  side.  They  vary  considerably  in  form  and  size,^  are 
seldom  symmetrical,  and  are  often  partially  subdivided  by  irregular  bony  laminae. 
Occasionally,  they  extend  into  the  basilar  part  of  the  occipital  nearly  as  far  as  the 
foramen  magnum.  They  begin  to  be  developed  before  birth,  and  are  of  a  consid- 
erable size  by  the  age  of  six.  They  are  partially  closed,  in  front  and  below,  by  two 
thin,  curved  plates  of  bone,  the  sphenoidal  conchse  (see  page  152),  leaving  in  the 
articulated  skull  a  round  opening  at  the  upper  part  of  each  sinus  by  which  it  com- 


ierygoid  canal 
Lateral  pterygoid  lamina 
Medial  -pterygoid  lamina 


Hamulus 


V 


Rostrum 
Fig.  147 — Sphenoid  bone.     Upper  and  posterior  surfaces. 

unicates  with  the  upper  and  back  part  of  the  nasal  cavity  and  occasionally  with 
the  posterior  ethmoidal  air  cells.  The  lateral  margin  of  the  anterior  surface  is 
serrated,  and  articulates  with  the  lamina  papyracea  of  the  ethmoid,  completing 
the  posterior  ethmoidal  cells;  the  lower  margin  articulates  with  the  orbital  process 
of  the  palatine  bone,  and  the  upper  with  the  orbital  plate  of  the  frontal  bone. 

The  inferior  surface  presents,  in  the  middle  line,  a  triangular  spine,  the  sphenoidal 
rostrum,  which  is  continuous  with  the  sphenoidal  crest  on  the  anterior  surface, 
and  is  received  in  a  deep  fissure  between  the  alee  of  the  vomer.  On  either  side  of 
the  rostrum  is  a  projecting  lamina,  the  vaginal  process,  directed  medialward  from 
he  base  of  the  medial  pterygoid  plate,  with  which  it  will  be  described. 

The  Great  Wings  (alee  viagnoe). — The  great  wings,  or  ali-sphenoids,  are  two 
strong  processes  of  bone,  which  arise  from  the  sides  of  the  body,  and  are  curved 
upward,  lateralward,  and  backward;  the  posterior  part  of  each  projects  as  a  tri- 
angular process  which  fits  into  the  angle  between  the  squama  and  the  petrous 

'  Aldren  Turner  (op.  cit.)  gives  the  following  as  their  average  measurements:  vertical  height,  '/s  inch;  antero-posterior 
<Jepth,  '/s  inch;  transverse  breadth,  Ji  inch. 


tak 


150  OSTEOLOGY 


portion  of  the  temporal  and  presents  at  its  apex  a  downwardly  directed  process, 
the  spina  angularis  {sphenoidal  spine). 

Surfaces. — ^The  superior  or  cerebral  surface  of  each  great  wing  (Fig.  145)  forms 
part  of  the  middle  fossa  of  the  skull ;  it  is  deeply  concave,  and  presents  depressions 
for  the  convolutions  of  the  temporal  lobe  of  the  brain.  At  its  anterior  and  medial 
part  is  a  circular  aperture,  the  foramen  rotundum,  for  the  transmission  of  the  maxil- 
lary nerve.  Behind  and  lateral  to  this  is  the  foramen  ovale,  for  the  transmission 
of  the  mandibular  nerve,  the  accessory  meningeal  artery,  and  sometimes  the 
lesser  superficial  petrosal  nerve. ^  Medial  to  the  foramen  ovale,  a  small  aperture, 
the  foramen  Vesalii,  may  occasionally  be  seen  opposite  the  root  of  the  pterygoid 
process;  it  opens  below  near  the  scaphoid  fossa,  and  transmits  a  small  vein  from 
the  cavernous  sinus.  Lastly,  in  the  posterior  angle,  near  to  and  in  front  of  the  spine, 
is  a  short  canal,  sometimes  double,  the  foramen  spinosum,  which  transmits  the 
middle  meningeal  vessels  and  a  recurrent  branch  from  the  mandibular  nerve. 

The  lateral  surface  (Fig.  146)  is  convex,  and  divided  by  a  transverse  ridge,  the 
infratemporal  crest,  into  two  portions.  The  superior  or  temporal  portion,  convex 
from  above  downward,  concave  from  before  backward,  forms  a  part  of  the  tem- 
poral fossa,  and  gives  attachment  to  the  Temporalis;  the  inferior  or  infratemporal, 
smaller  in  size  and  concave,  enters  into  the  formation  of  the  infratemporal  fossa, 
and,  together  with  the  infratemporal  crest,  affords  attachment  to  the  Pterygoideus 
externus.  It  is  pierced  by  the  foramen  ovale  and  foramen  spinosum,  and  at  its 
posterior  part  is  the  spina  angularis,  which  is  frequently  grooved  on  its  medial 
surface  for  the  chorda  tympani  nerve.  To  the  spina  angularis  are  attached  the 
sphenomandibular  ligament  and  the  Tensor  veli  palatini.  Medial  to  the  anterior 
extremity  of  the  infratemporal  crest  is  a  triangular  process  which  serves  to  increase 
the  attachment  of  the  Pterygoideus  externus;  extending  downward  and  medialward 
from  this  process  on  to  the  front  part  of  the  lateral  pterygoid  plate  is  a  ridge  which 
forms  the  anterior  limit  of  the  infratemporal  surface,  and,  in  the  articulated  skull, 
the  posterior  boundary  of  the  pterygomaxillary  fissure. 

The  orbital  surface  of  the  great  wing  (Fig.  146),  smooth,  and  quadrilateral  in 
shape,  is  directed  forward  and  medialward  and  forms  the  posterior  part  of  the 
lateral  wall  of  the  orbit.  Its  upper  serrated  edge  articulates  with  the  orbital  plate 
of  the  frontal.  Its  inferior  rounded  border  forms  the  postero-lateral  boundary  of 
the  inferior  orbital  fissure.  Its  medial  sharp  margin  forms  the  lower  boundary 
of  the  superior  orbital  fissure  and  has  projecting  from  about  its  center  a  little 
tubercle  which  gives  attachment  to  the  inferior  head  of  the  Rectus  lateralis  oculi; 
at  the  upper  part  of  this  margin  is  a  notch  for  the  transmission  of  a  recurrent 
branch  of  the  lacrimal  artery.  Its  lateral  margin  is  serrated  and  articulates  with 
the  zygomatic  bone.  Below  the  medial  end  of  the  superior  orbital  fissure  is  a 
grooved  surface,  which  forms  the  posterior  wall  of  the  pterygopalatine  fossa, 
and  is  pierced  by  the  foramen  rotundum. 

Margin  (Fig.  145). — Commencing  from  behind,  that  portion  of  the  circum- 
ference of  the  great  wing  which  extends  from  the  body  to  the  spine  is  irregular. 
Its  medial  half  forms  the  anterior  boundary  of  the  foramen  lacerum,  and  presents 
the  posterior  aperture  of  the  pterygoid  canal  for  the  passage  of  the  correspond- 
ing nerve  and  artery.  Its  lateral  half  articulates,  by  means  of  a  synchondrosis, 
with  the  petrous  portion  of  the  temporal,  and  between  the  two  bones  on  the 
under  surface  of  the  skull,  is  a  furrow,  the  sulcus  tubae,  for  the  lodgement  of  the 
cartilaginous  part  of  the  auditory  tube.  In  front  of  the  spine  the  circumference 
presents  a  concave,  serrated  edge,  bevelled  at  the  expense  of  the  inner  table  below, 
and  of  the  outer  table  above,  for  articulation  with  the  temporal  squama.  At 
the  tip  of  the  great  wing  is  a  triangular  portion,  bevelled  at  the  expense  of  the 

1  The  lesser  superficial  petrosal  nerve  sometimes  passes  through  a  special  canal  (canaliculus  innominatus  of  Arnold) 
situated  medial  to  the  foramen  spinosum. 


I 


THE  SPHENOID  BONE  151 


internal  surface,  for  articulation  with  the  sphenoidal  angle  of  the  parietal  bone; 
this  region  is  named  the  pterion.  Medial  to  this  is  a  triangular,  serrated  surface, 
for  articulation  with  the  frontal  bone;  this  surface  is  continuous  medially  with 
the  sharp  edge,  w^hich  forms  the  lower  boundary  of  the  superior  orbital  fissure, 
and  laterally  with  the  serrated  margin  for  articulation  with  the  zygomatic  bone. 

The  Small  Wings  {ales  parvcp). — The  small  wings  or  orbito-sphenoids  are  two 
thin  triangular  plates,  which  arise  from  the  upper  and  anterior  parts  of  the  body, 
and,  projecting  lateralward,  end  in  sharp  points  (Fig.  145). 

Surfaces. — The  superior  surface  of  each  is  flat,  and  supports  part  of  the  frontal 
lobe  of  the  brain.  The  inferior  surface  forms  the  back  part  of  the  roof  of  the  orbit, 
and  the  upper  boundary  of  the  superior  orbital  fissure.  This  fissure  is  of  a  triangular 
form,  and  leads  from  the  cavity  of  the  cranium  into  that  of  the  orbit:  it  is  bounded 

P  medially  by  the  body;  above,  by  the  small  wing;  below,  by  the  medial  margin  of 
the  orbital  surface  of  the  great  wing;  and  is  completed  laterally  by  the  frontal 
bone.     It  transmits  the  oculomotor,  trochlear,  and  abducent  nerves,  the  three 
^_  branches  of  the  ophthalmic  division  of  the  trigeminal  nerve,  some  filaments  from 
^■the  cavernous  plexus  of  the  sympathetic,  the  orbital  branch  of  the  middle  menin- 
^^  geal  artery,  a  recurrent  branch  from  the  lacrimal  artery  to  the  dura  mater,  and  the 
ophthalmic  vein. 

Borders. — The  anterior  border  is  serrated  for  articulation  with  the  frontal  bone. 
The  posterior  border,  smooth  and  rounded,  is  received  into  the  lateral  fissure  of 
the  brain;  the  medial  end  of  this  border  forms  the  anterior  clinoid  process,  which 
gives  attachment  to  the  tentorium  cerebelli;  it  is  sometimes  joined  to  the  middle 
clinoid  process  by  a  spicule  of  bone,  and  when  this  occurs  the  termination  of  the 
groove  for  the  internal  carotid  artery  is  converted  into  a  foramen  (carotico-clinoid) . 

rThe  small  wing  is  connected  to  the  body  by  two  roots,  the  upper  thin  and  flat, 
Ithe  lower  thick  and  triangular;  between  the  two  roots  is  the  optic  foramen,  for  the 
transmission  of  the  optic  nerve  and  ophthalmic  artery. 
Pterygoid  Processes  {processus  pterygoidei). — The  pterygoid  processes,  one  on 
either  side,  descend  perpendicularly  from  the  regions  where  the  body  and  great 
wings  unite.    Each  process  consists  of  a  medial  and  a  lateral  plate,  the  upper  parts 
of  which  are  fused  anteriorly ;  a  vertical  sulcus,  the  pterygopalatine  groove,  descends 
on  the  front  of  the  line  of  fusion.    The  plates  are  separated  below  by  an  angular 
L    cleft,  the  pterygoid  fissure,  the  margins  of  which  are  rough  for  articulation  with 
Hlthe  pyramidal  process  of  the  palatine  bone.    The  two  plates  diverge  behind  and 
»    enclose  between  them  a  V-shaped  fossa,  the  pterygoid  fossa,  which  contains  the 
P     Pterygoideus  internus  and  Tensor  veli  palatini.    Above  this  fossa  is  a  small,  oval, 
shallow  depression,  the  scaphoid  fossa,  which  gives  origin  to  the  Tensor  veli  palatini. 
,The  anterior  surface  of  the  pterygoid  process  is  broad  and  triangular  near  its 
iroot,  where  it  forms  the  posterior  wall  of  the  pterygopalatine  fossa  and  presents 
the  anterior  orifice  of  the  pterygoid  canal. 

Lateral  Pterygoid  Plate. — The  lateral  pterygoid  plate  is  broad,  thin,  and  everted; 
its  lateral  surface  forms  part  of  the  medial  wall  of  the  infratemporal  fossa,  and 
gives  attachment  to  the  Pterygoideus  externus;  its  medial  surface  forms  part  of 
the  pterygoid  fossa,  and  gives  attachment  to  the  Pterygoideus  internus. 

Medial  Pterygoid  Plate. — The  medial  pterygoid  plate  is  narrower  and  longer 
than  the  lateral ;  it  curves  lateralward  at  its  lower  extremity  into  a  hook-like  pro- 

fcess,  the  pterygoid  hamulus,  around  which  the  tendon  of  the  Tensor  veli  palatini 
glides.  The  lateral  surface  of  this  plate  forms  part  of  the  pterygoid  fossa,  the 
medial  surface  constitutes  the  lateral  boundary  of  the  choana  or  posterior  aperture 
of  the  corresponding  nasal  cavity.  Superiorly  the  medial  plate  is  prolonged  on  to 
the  under  surface  of  the  body  as  a  thin  lamina,  named  the  vaginal  process,  which 
articulates  in  front  with  the  sphenoidal  process  of  the  palatine  and  behind  this 
with  the  ala  of  the  vomer.    The  angular  prominence  between  the  posterior  margin 


I 


OSTEOLOGY 

of  the  vaginal  process  and  the  medial  border  of  the  scaphoid  fossa  is  named  the 
pterygoid  tubercle,  and  immediately  above  this  is  the  posterior  opening  of  tbe 
pterygoid  canal.  On  the  under  surface  of  the  vaginal  process  is  a  furrow,  which 
is  converted  into  a  canal  by  the  sphenoidal  process  of  the  palatine  bone,  for  the 
transmission  of  the  pharyngeal  branch  of  the  internal  maxillary  artery  and  the 
pharyngeal  nerve  from  the  sphenopalatine  ganglion.  The  pharyngeal  aponeurosis 
is  attached  to  the  entire  length  of  the  posterior  edge  of  the  medial  plate,  and  the 
Constrictor  pharyngis  superior  takes  origin  from  its  lower  third.  Projecting 
backward  from  near  the  middle  of  the  posterior  edge  of  this  plate  is  an  angular 
process,  the  processus  tubarius,  which  supports  the  pharyngeal  end  of  the  auditory 
tube.  The  anterior  margin  of  the  plate  articulates  with  the  posterior  border  of 
the  vertical  part  of  the  palatine  bone. 

The  Sphenoidal  Conchse  (conchce  sphenoidales;  sphenoidal  turbinated  processes). 
— The  sphenoidal  conchse  are  two  thin,  curved  plates,  situated  at  the  anterior 
and  lower  part  of  the  body  of  the  sphenoid.  An  aperture  of  variable  size  exists 
in  the  anterior  wall  of  each,  and  through  this  the  sphenoidal  sinus  opens  into  the 
nasal  cavity.  Each  is  irregular  in  form,  and  tapers  to  a  point  behind,  being  broader 
and  thinner  in  front.  Its  upper  surface  is  concave,  and  looks  toward  the  cavity 
of  the  sinus;  its  under  surface  is  convex,  and  forms  part  of  the  roof  of  the  corre- 
sponding nasal  cavity.  Each  bone  articulates  in  front  with  the  ethmoid,  laterally 
with  the  palatine;  its  pointed  posterior  extremity  is  placed  above  the  vomer, 
and  is  received  between  the  root  of  the  pterygoid  process  laterally  and  the  rostrum 
of  the  sphenoid  medially.  A  small  portion  of  the  sphenoidal  concha  sometimes 
enters  into  the  formation  of  the  medial  wall  of  the  orbit,  between  the  lamina 
papyracea  of  the  ethmoid  in  front,  the  orbital  plate  of  the  palatine  below,  and  the 
frontal  bone  above. 


Ossification. — Until  the  seventh  or  eighth  month  of  fetal  life  the  body  of  the  sphenoid  consists 
of  two  parts,  viz.,  one  in  front  of  the  tuberculum  sella;,  the  presphenoid,  with  which  the  small 
wings  are  continuous;  the  other,  comprising  the  sella  turcica  and  dorsum  sellae,  the  posisphenoid, 

with  which  are  associated  the  great 
wings,  and  pterygoid  processes.  The 
greater  part  of  the  bone  is  ossified  in 
cartilage.  There  are  fourteen  centers 
in  all,  six  for  the  presphenoid  and  eight 
for  the  postsphenoid. 

Presphenoid. — About  the  ninth  week 
of  fetal  hfe  an  ossific  center  appears  for 
each  of  the  small  wings  (orbitosphenoids) 
just  lateral  to  the  optic  foramen;  shortly 
afterward  two  nuclei  appear  in  the  pre- 
sphenoid part  of  the  body.  The  sphe- 
noidal concha;  are  each  developed  from 
a  center  which  makes  its  appearance  about  the  fifth  month  ;i  at  birth  they  consist  of  small 
triangular  laminae,  and  it  is  not  until  the  third  year  that  they  become  hollowed  out  and  cone- 
shaped;  about  the  fourth  year  they  fuse  with  the  labyrinths  of  the  ethmoid,  and  between  the 
ninth  and  twelfth  years  they  unite  with  the  sphenoid. 

Postsphenoid. — The  first  ossific  nuclei  are  those  for  the  great  wings  (ali-sphenoids)-.  One  makes 
its  appearance  in  each  wing  between  the  foramen  rotundum  and  foramen  ovale  about  the  eighth 
week.  The  orbital  plate  and  that  part  of  the  sphenoid  which  is  found  in  the  temporal  fossa,  as 
well  as  the  lateral  pterygoid  plate,  are  ossified  in  membrane  (Fawcett)^  Soon  after,  the  centers 
for  the  postsphenoid  part  of  the  body  appear,  one  on  either  side  of  the  sella  turcica,  and  become 
blended  together  about  the  middle  of  fetal  life.  Each  medial  pterygoid  plate  (with  the  exception 
of  its  hamulus)  is  ossified  in  membrane,  and  its  center  probably  appears  about  the  ninth  or  tenth 
week;  the  hamulus  becomes  chondrified  during  the  third  month,  and  almost  at  once  undergoes 


Fig.  148. — Sphenoid  bone  at  birth.     Posterior  aspect. 


1  According  to  Cleland,  each  sphenoidal  concha  is  ossified  from  four  centers. 

2  Mall,  Am.  Jour.  Anat.,  1906,  states  that  the  pterygoid  center  appears  first  in  an  embryo  fifty-seven  days  old. 
*  Journal  of  Anatomy  and  Physiology,  1910,  vol.  xliv. 


IF 


THE  ETHMOID  BONE 


153 


ossification  (Fawcett).^  The  medial  joins  the  lateral  pterygoid  plate  about  the  sixth  month. 
About  the  fourth  month  a  center  appears  for  each  lingula  and  speedily  joins  the  rest  of  the  bone. 

The  presphenoid  is  united  to  the  postsphenoid  about  the  eighth  month,  and  at  birth  the  bone 
is  in  three  pieces  (Fig.  148) :  a  central,  consisting  of  the  body  and  small  wings,  and  two  lateral, 
each  comprising  a  great  wing  and  pterygoid  process.  In  the  first  year  after  birth  the  great  wings 
and  body  unite,  and  the  small  wings  extend  inward  above  the  anterior  part  of  the  body,  and, 
meeting  with  each  other  in  the  middle  hne,  form  an  elevated  smooth  surface,  termed  the  jugum 
sphenoidale.  By  the  twenty-fifth  year  the  sphenoid  and  occipital  are  completely  fused.  Between 
the  pre-  and  postsphenoid  there  are  occasionally  seen  the  remains  of  a  canal,  the  canalis  cranio- 
pharyngeus,  through  which,  in  early  fetal  Hfe,  the  hypophyseal  diverticulum  of  the  buccal  ecto- 
derm is  transmitted. 

The  sphenoidal  sinuses  are  present  as  minute  cavities  at  the  time  of  birth  (Onodi),  but  do  not 
attain  their  full  size  until  after  puberty. 

Intrinsic  Ligaments  of  the  Sphenoid. — The  more  important  of  these  are :  the  pterygospinous, 
stretching  between  the  spina  angularis  and  the  lateral  pterygoid  plate  (see  cervical  fascia);  the 
iiiterclinoid,  a  fibrous  process  joining  the  anterior  to  the  posterior  clinoid  process;  and  the 
curoticoclinoid ,  connecting  the  anterior  to  the  middle  clinoid  process.  These  ligaments  occa- 
sionally ossify. 

Articulations. — The  sphenoid  articulates  with  twelve  bones:  four  single,  the  vomer,  ethmoid, 
frontal,  and  occipital;  and  four  paired,  the  parietal,  temporal,  zygomatic,  and  palatine.- 

The  Ethmoid  Bone  (Os  Ethmoidale). 

The  ethmoid  bone  is  exceedingly  light  and  spongy,  and  cubical  in  shape;  it 
is  situated  at  the  anterior  part  of  the  base  of  the  cranium,  between  the  two  orbits, 
fit  the  roof  of  the  nose,  and  contributes  to  each  of  these  cavities.  It  consists  of 
four  parts:  a  horizontal  or  cribriform  plate,  forming  part  of  the  base  of  the  cranium; 
a  perpendicular  plate,  constituting  part  of  the  nasal  septum;  and  two  lateral  masses 
or  labyrinths. 

Cribiform  Plate  {lamina  cribrosa;  horizontal  lamina). — The  cribriform  plate 
(Fig.  149)  is  received  into  the  ethmoidal  notch  of  the  frontal  bone  and  roofs  in 
ihe  nasal  cavities.  Projecting  upward  from  the  middle  line  of  this  plate  is  a  thick, 
smooth,  triangular  process,  the  crista  galli,  so  called  from  its  resemblance  to  a 
cock's  comb.  The  long  thin  posterior  border  of  the  crista  galli  serves  for  the 
attachment  of  the  falx  cerebri. 
ts  anterior  border,  short  and 
1  hick,  articulates  with  the  frontal 
bone,  and  presents  two  small  pro- 
.ecting  alae,  which  are  received 
into  corresponding  depressions  in 
:he  frontal  bone  and  complete 
:he  foramen  cecum.  Its  sides  are 
:5mooth,  and  sometimes  bulging 
'rom  the  presence  of  a  small  air 
dnus  in  the  interior.  On  either 
side  of  the  crista  galli,  the  cribri- 
form plate  is  narrow  and  deeply 
grooved;  it  supports  the  olfactory 
bulb  and  is  perforated  by  fora-. 
mina  for  the  passage  of  the  olfac- 
tory nerves.  The  foramina  in  the 
middle  of  the  groove  are  small 
and  transmit  the   nerves  to  the 

roof  of  the  nasal  cavity;  those  at  the  medial  and  lateral  parts  of  the  groove  are 
larger — the  former  transmit  the  nerves  to  the  upper  part  of  the  nasal  septum, 
the  latter  those  to  the  superior  nasal  concha.    At  the  front  part  of  the  cribriform 

1  Anatomischer  Anzeiger,  March,  1905. 
It  also  sometimes  articulates  with  the  tuberosity  of  the  maxilla  (see  page  159). 


Perpendicular  plate 
Ala 


Crista  gain 


Cribriform  plate 

Anterior  ethmoidal 
groove 


Posterior  ethmoidal 
groove 


Fig.  149. — Ethmoid  bone  from  above. 


154 


OSTEOLOGY 


I 


plate,  on  either  side  of  the  crista  galli,  is  a  small  fissure  which  is  occupied  bj  a 
process  of  dura  mater.  Lateral  to  this  fissure  is  a  notch  or  foramen  which  trans- 
mits the  nasociliary  nerve;  from  this  notch  a  groove  extends  backward  to  the 
anterior  ethmoidal  foramen. 


Fig.    150. — Perpendicular  plate  of  ethmoid.     Shown  by  removing  the  right  labyrinth. 

Perpendicular  Plate  (lamina  perpendicularis;  vertical  plate). — The  perpendicular 
plate  (Figs.  150,  151)  is  a  thin,  flattened  lamina,  polygonal  in  form,  which  descends 
from  the  under  surface  of  the  cribriform  plate,  and  assists  in  forming  the  septum 
of  the  nose;  it  is  generally  deflected  a  little  to  one  or  other  side.  The  anterior  border 
articulates  with  the  spine  of  the  frontal  bone  and  the  crest  of  the  nasal  bones. 
The  posterior  border  articulates  by  its  upper  half  with  the  sphenoidal  crest,  by  its 
lower  with  the  vomer.  The  inferior  border  is  thicker  than  the  posterior,  and  serves 
for  the  attachment  of  the  septal  cartilage  of  the  nose.  The  surfaces  of  the  plate 
are  smooth,  except  above,  where  numerous  grooves  and  canals  are  seen;  these 
lead  from  the  medial  foramina  on  the  cribriform  plate  and  lodge  filaments  of  the 
olfactory  nerves. 

The  Labyrinth  or  Lateral  Mass  (labyrinthus  ethmoidalis)  consists  of  a  number 
of  thin-walled  cellular  cavities,  the  ethmoidal  cells,   arranged  in  three  groups, 

anterior,  middle,  and  posterior,  and  inter- 
posed between  two  vertical  plates  of  bone; 
the  lateral  plate  forms  part  of  the  orbit, 
the  medial,  part  of  the  corresponding 
nasal  cavity.  In  the  disarticulated  bone 
many  of  these  cells  are  opened  into,  but 
when  the  bones  are  articulated,  they  are 
closed  in  at  every  part,  except  where 
they  open  into  the  nasal  cavity. 

Surfaces. — The  upper  surface  of  the  laby- 
rinth (Fig.  149)  presents  a  number  of 
half-broken  cells,  the  walls  of  which  are 
completed,  in  the  articulated  skull,  by 
the  edges  of  the  ethmoidal  notch  of  the 
frontal  bone.  Crossing  this  surface  are 
two  grooves,  converted  into  canals  by  articulation  with  the  frontal;  they  are  the 
anterior  and  posterior  ethmoidal  canals,  and  open  on  the  inner  wall  of  the  orbit. 
The  posterior  surface  presents  large  irregular  cellular  cavities,  which  are  closed  in 


Crista  galli 


Labyrinth 

Superior  nasal 

concha 
Superior  meatus 

Uncinate  process 

Middle  nasal  concha 
■  Perpendicular  plate 
Fig.   151. — Ethmoid  bone  from  behind. 


I 


THE  ETHMOID  BONE 


155 


by  articulation  with  the  sphenoidal  concha  and  orbital  process  of  the  palatine. 
The  lateral  surface  (Fig.  152)  is  formed  of  a  thin,  smooth,  oblong  plate,  the  lamina 
papyracea  {os  planum),  which  covers  in  the  middle  and  posterior  ethmoidal  cells 


Ethmoidal 
cells 


Perpendicviar 

plate 


Uncinate  process 


Fig.   152. — Ethmoid  bone  from  the  right  side. 


and  forms  a  large  part  of  the  medial  wall  of  the  orbit;  it  articulates  above  with 
the  orbital  plate  of  the  frontal  bone,  below  with  the  maxilla  and  orbital  process 
of  the  palatine,  in  front  with  the  lacrimal,  and  behind  with  the  sphenoid. 

In  front  of  the  lamina  papyracea  are  some  broken  air  cells  which  are  overlapped 
and  completed  by  the  lacrimal  bone  and  the  frontal  process  of  the  maxilla.    A 


Frontal  simis 


Crista  gain 


Sella  turcica 


Openings  into 
maxillary  sinus 
Medial  pterygoid  plate 
Hamulus 


Lateral  wall  of  nasal  cavity,  showing  ethmoid  bone  in  position. 


I 


ed  lamina,  the  uncinate  process,  projects  downward  and  backward  from  this 
part  of  the  labyrinth;  it  forms  a  small  part  of  the  medial  wall  of  the  maxillary 
sinus,  and  articulates  with  the  ethmoidal  process  of  the  inferior  nasal  concha. 


156 


I 


The  medial  surface  of  the  labyrinth  (Fig.  153)  forms  part  of  the  lateral  ^all 
of  the  corresponding  nasal  cavity.  It  consists  of  a  thin  lamella,  which  descends 
from  the  under  surface  of  the  cribriform  plate,  and  ends  below  in  a  free,  convoluted 
margin,  the  middle  nasal  concha.  It  is  rough,  and  marked  above  by  numerous 
grooves,  directed  nearly  vertically  downward  from  the  cribriform  plate;  they 
lodge  branches  of  the  olfactory  nerves,  which  are  distributed  to  the  mucous  mem- 
brane covering  the  superior  nasal  concha.  The  back  part  of  the  surface  is  sub- 
divided by  a  narrow  oblique  fissure,  the  superior  meatus  of  the  nose,  bounded  above 
by  a  thin,  curved  plate,  the  superior  nasal  concha;  the  posterior  ethmoidal  cells 
open  into  this  meatus.  Below,  and  in  front  of  the  superior  meatus,  is  the  con^'ex 
surface  of  the  middle  nasal  concha;  it  extends  along  the  whole  length  of  the  medial 
surface  of  the  labyrinth,  and  its  lower  margin  is  free  and  thick.  The  lateral  surface 
of  the  middle  concha  is  concave,  and  assists  in  forming  the  middle  meatus  of  the 
nose.  The  middle  ethmoidal  cells  open  into  the  central  part  of  this  meatus,  and  a 
sinuous  passage,  termed  the  infundibulum,  extends  upward  and  forward  through 
the  labyrinth  and  communicates  with  the  anterior  ethmoidal  cells,  and  in  about 
50  per  cent,  of  skulls  is  continued  upward  as  the  frontonasal  duct  into  the  frontal 
sinus. 

Ossification. — The  ethmoid  is  ossified  in  the  cartilage  of  the  nasal  capsule  by  three  centers: 
one  for  the  perpendicular  plate,  and  one  for  each  labyrinth. 

The  labyrinths  are  first  developed,  ossific  granules  making  their  appearance  in  the  region  of 
the  lamina  papyracea  between  the  fourth  and  fifth  months  of  fetal  life,  and  extending  into  the 
conchse.  At  birth,  the  bone  consists  of  the  two  labyrinths,  which  are  small  and  ill-developed. 
During  the  first  year  after  birth,  the  perpendicular  plate  and  crista  galli  begin  to  ossify  from  a 
single  center,  and  are  joined  to  the  labyrinths  about  the  beginning  of  the  second  year.  The 
cribriform  plate  is  ossified  partly  from  the  perpendicular  plate  and  partly  from  the  labyrinths. 
The  development  of  the  ethmoidal  cells  begins  during  fetal  life. 

Articulations. — The  ethmoid  articulates  -with,  fifteen  bones:  four  of  the  cranium — the  frontal, 
the  sphenoid,  and  the  two  sphenoidal  conchae;  and  eleven  of  the  face — the  two  nasals,  two  maxillae, 
two  lacrimals,  two  palatines,  two  inferior  nasal  conchae,  and  the  vomer. 

Sutnral  or  Wormian^  Bones. — In  addition  to  the  usual  centers  of  ossification  of  the  cranium, 
others  may  occur  in  the  course  of  the  sutures,  giving  rise  to  irregular,  isolated  bones,  termed 
suiural  or  Wormian  hones.  They  occur  most  frequently  in  the  course  of  the  lambdoidal  suture, 
but  are  occasionally  seen  at  the  fontanelles,  especially  the  posterior.  One,  the  pterion  ossicle, 
sometimes  exists  between  the  sphenoidal  angle  of  the  parietal  and  the  great  wing  of  the  sphenoid. 
They  have  a  tendency  to  be  more  or  less  symmetrical  on  the  two  sides  of  the  skull,  and  vary 
much  in  size.  Their  number  is  generally  Hmited  to  two  or  three;  but  more  than  a  hundred  have 
been  found  in  the  skull  of  an  adult  hydrocephalic  subject. 


THE  FACIAL  BONES  (OSSA  FACIEI). 

The  Nasal  Bones  (Ossa  Nasalia) . 

The  nasal  bones  are  two  small  oblong  bones,  varying  in  size  and  form  in  different 
individuals;  they  are  placed  side  by  side  at  the  middle  and  upper  part  of  the  face, 
and  form,  by  their  junction,  "the  bridge"  of  the  nose  (Fig.  190).  Each  has  two 
surfaces  and  four  borders. 

Surfaces. — The  outer  surface  (Fig.  155)  is  concavoconvex  from  above  downward, 
convex  from  side  to  side;  it  is  covered  by  the  Procerus  and  Compressor  naris,  and 
perforated  about  its  center  by  a  foramen,  for  the  transmission  of  a  small  vein. 
The  inner  surface  (Fig.  150)  is  concave  from  side  to  side,  and  is  traversed  from  above 
downward,  by  a  groove  for  the  passage  of  a  branch  of  the  nasociliary  nerve. 

Borders. — The  superior  border  is  narrow,  thick,  and  serrated  for  articulation  with 
the  nasal  notch  of  the  frontal  bone.    The  inferior  border  is  thin,  and  gives  attach- 

'  Ole  Worm,  Professor  of  Anatomy  at  Copenhagen,  1624-1639,  was  erroneously  supposed  to  have  given  the  first 
detailed  description  of  these  bones. 


I 


THE  MAXILLA 


157 


nient  to  the  lateral  cartilage  of  the  nose;  near  its  middle  is  a  notch  which  marks 
the  end  of  the  groove  just  referred  to.  The  lateral  border  is  serrated,  bevelled 
at  the  expense  of  the  inner  surface  above,  and  of  the  outer  below,  to  articulate 
Mith  the  frontal  process  of  the  maxilla.    The  medial  border,  thicker  above  than 


Fossa  Jor  lacrimal  sac 


Infraorbital 
foramen 


Fig.  154. — Articulation  of  nasal  and  lacrimal  bones  with  maxilla. 

Delow,  articulates  with  its  fellow  of  the  opposite  side,  and  is  prolonged  behind  into 
a,  vertical  crest,  which  forms  part  of  the  nasal  septum:  this  crest  articulates,  from 
above  downward,  with  the  spine  of  the  frontal,  the  perpendicular  plate  of  the 
ethmoid,  and  the  septal  cartilage  of  the  nose. 


Foramen 
for  vein 


yitt^ 


— Right  nasal  bone.     Outer  surface. 


Crest 


Groove 
for  nerve 


Fig.  156. — Right  nasal  bone.     Inner  surface. 


Ossification. — Each  bone  is  ossified  from  one  center,  which  appears  at  the  beginning  of  the 
third  month  of  fetal  hfe  in  the  membrane  overlying  the  front  part  of  the  cartilaginous  nasal 
capsule. 

Articulations. — The  nasal  articulates  with  foiu-  bones:  two  of  the  cranium,  the  frontal  and 
ethmoid,  and  two  of  the  face,  the  opposite  nasal  and  the  maxilla. 

The  Maxillae  (Upper  Jaw). 

The  maxillae  are  the  largest  bones  of  the  face,  excepting  the  mandible,  and 
form,  by  their  union,  the  whole  of  the  upper  jaw.    Each  assists  in  forming  the 


■ 


158 


OSTEOLOGY 


I 


boundaries  of  three  cavities,  viz.,  the  roof  of  the  mouth,  the  floor  and  lateral 
wall  of  the  nose  and  the  floor  of  the  orbit;  it  also  enters  into  the  formation  of  two 
fossae,  the  infratemporal  and  pterygopalatine,  and  two  fissures,  the  inferior  orbital 
and  pterygomaxillary. 

Each  bone  consists  of  a  body  and  four  processes — zygomatic,  frontal,  alveolar, 
and  palatine. 

The  Body  {corpus  maxilla;). — The  body  is  somewhat  pyramidal  in  shape,  and 
contains  a  large  cavity,  the  maxillary  sinus  (antrum  of  Highmore).  It  has  four 
surfaces — an  anterior,  a  posterior  or  infratemporal,  a  superior  or  orbital,  and.  a 
medial  or  nasal. 

Surfaces. — The  anterior  surface  (Fig,  157)  is  directed  forward  and  lateralward. 
It  presents  at  its  lower  part  a  series  of  eminences  corresponding  to  the  positions 
of  the  roots  of  the  teeth.  Just  above  those  of  the  incisor  teeth  is  a  depression, 
the  incisive  fossa,  which  gives  origin  to  the  Depressor  alaj  nasi;  to  the  alveolar 
border  below  the  fossa  is  attached  a  slip  of  the  Orbicularis  oris;  above  and  a  little 


Med.  jxi 


DlIiATATOE  NARIS  POSTERIOR 


Incisive  fossa 


Alveolar  canals 


Maxillary  tvberosity 


Fia.  157. — Left  maxilla.     Outer  surface. 

lateral  to  it,  the  Nasalis  arises.  Lateral  to  the  incisive  fossa  is  another  depression, 
the  canine  fossa;  it  is  larger  and  deeper  than  the  incisive  fossa,  and  is  separated 
from  it  by  a  vertical  ridge,  the  canine  eminence,  corresponding  to  the  socket  of 
the  canine  tooth;  the  canine  fossa  gives  origin  to  the  Caninus,  Above  the  fossa 
is  the  infraorbital  foramen,  the  end  of  the  infraorbital  canal;  it  transmits  the  infra- 
orbital vessels  and  nerve.  Above  the  foramen  is  the  margin  of  the  orbit,  which 
affords  attachment  to  part  of  the  Quadratus  labii  superioris.  Medially,  the  anterior 
surface  is  limited  by  a  deep  concavity,  the  nasal  notch,  the  margin  of  which  gives 
attachment  to  the  Dilatator  naris  posterior  and  ends  below  in  a  pointed  process, 
which  with  its  fellow  of  the  opposite  side  forms  the  anterior  nasal  spine. 

The  infratemporal  surface  (Fig,  157)  is  convex,*  directed  backward  and  lateral- 
ward,  and  forms  part  of  the  infratemporal  fossa.  It  is  separated  from  the  anterior 
surface  by  the  zygomatic  process  and  by  a  strong  ridge,  extending  upward  from 
the  socket  of  the  first  molar  tooth.  It  is  pierced  about  its  center  by  the  apertures 
of  the  alveolar  canals,  which  transmit  the  posterior  superior  alveolar  vessels  and 
nerves.    At  the  lower  part  of  this  surface  is  a  rounded  eminence,  the  maxillary 


THE  MAXILLA 


159 


tuberosity,  especially  prominent  after  the  growth  of  the  wisdom  tooth;  it  is  rough 
on  its  lateral  side  for  articulation  with  the  pyramidal  process  of  the  palatine  bone 
and  in  some  cases  articulates  with  the  lateral  pterygoid  plate  of  the  sphenoid. 
It  gives  origin  to  a  few  fibers  of  the  Pterygoideus  internus.  Immediately  above 
this  is  a  smooth  surface,  which  forms  the  anterior  boundary  of  the  pterygopalatine 
fossa,  and  presents  a  groove,  for  the  maxillary  nerve;  this  groove  is  directed  lateral- 
ward  and  slightly  upward,  and  is  continuous  with  the  infraorbital  groove  on  the 
orbital  surface. 

The  orbital  surface  (Fig.  157)  is  smooth  and  triangular,  and  forms  the  greater 
part  of  the  floor  of  the  orbit.  It  is  bounded  medially  by  an  irregular  margin  which 
in  front  presents  a  notch,  the  lacrimal  notch;  behind  this  notch  the  margin  articu- 
lates with  the  lacrimal,  the  lamina  papyracea  of  the  ethmoid  and  the  orbital  process 
of  the  palatine.  It  is  bounded  behind  by  a  smooth  rounded  edge  which  forms 
the  anterior  margin  of  the  inferior  orbital  fissure,  and  sometimes  articulates  at 
its  lateral  extremity  with  the  orbital  surface  of  the  great  wing  of  the  sphenoid. 


With  frontal 


Bones  partially  closing  orifice  of  sinus 
marked  in  red 


Ethmoid — 


With  nasal  hone 


inferior  nasal  coiicha— 
Palatine—. 


Ant.  nasal  spine 


Bristle  passed 
through  incisive 
canxd 


Fig.   158. — Left  maxilla.     Nasal  surface. 


It  is  limited  in  front  by  part  of  the  circumference  of  the  orbit,  which  is  continuous 
^aedially  with  the  frontal  process,  and  laterally  with  the  zyogmatic  process.  Near 
the  middle  of  the  posterior  part  of  the  orbital  surface  is  the  infraorbital  groove, 
for  the  passage  of  the  infraorbital  vessels  and  nerve.  The  groove  begins  at  the 
middle  of  the  posterior  border,  where  it  is  continuous  with  that  near  the  upper 
edge  of  the  infratemporal  surface,  and,  passing  forward,  ends  in  a  canal,  which 
subdivides  into  two  branches.  One  of  the  canals,  the  infraorbital  canal,  opens 
just  below  the  margin  of  the  orbit;  the  other,  which  is  smaller,  runs  downward  in 
the  substance  of  the  anterior  wall  of  the  maxillary  sinus,  and  transmits  the  anterior 
superior  alveolar  vessels  and  nerve  to  the  front  teeth  of  the  maxilla.  From  the 
back  part  of  the  infraorbital  canal,  a  second  small  canal  is  sometimes  given  off;  it 
runs  downward  in  the  lateral  wall  of  the  sinus,  and  conveys  the  middle  alveolar 
nerve  to  the  premolar  teeth.  At  the  medial  and  forepart  of  the  orbital  surface, 
just  lateral  to  the  lacrimal  groove,  is  a  depression,  which  gives  origin  to  the  Obliquus 
oculi  inferior. 


i 


160 


OSTEOLOGY 


The  nasal  siirface  (Fig.  158)  presents  a  large,  irregular  opening  leading  into  tbe 
maxillary  sinus.  At  the  upper  border  of  this  aperture  are  some  broken  air  cells, 
which,  in  the  articulated  skull,  are  closed  in  by  the  ethmoid  and  lacrimal  bones. 
Below  the  aperture  is  a  smooth  concavity  which  forms  part  of  the  inferior  meatus 
of  the  nasal  cavity,  and  behind  it  is  a  rough  surface  for  articulation  with  the  per- 
pendicular part  of  the  palatine  bone;  this  surface  is  traversed  by  a  groove,  com- 
mencing near  the  middle  of  the  posterior  border  and  running  obliquely  downward 
and  forward;  the  groove  is  converted  into  a  canal,  the  pterygopalatine  canal,  by  the 
palatine  bone.  In  front  of  the  opening  of  the  sinus  is  a  deep  groove,  the  lacrimal 
groove,  which  is  converted  into  the  nasolacrimal  canal,  by  the  lacrimal  bone  and 
inferior  nasal  concha;  this  canal  opens  into  the  inferior  meatus  of  the  nose  and 
transmits  the  nasolacrimal  duct.  More  anteriorly  is  an  oblique  ridge,  the  conchal 
crest,  for  articulation  with  the  inferior  nasal  concha.  The  shallow  concavity  aboAe 
this  ridge  forms  part  of  the  atrium  of  the  middle  meatus  of  the  nose,  and  that 
below  it,  part  of  the  inferior  meatus. 


Anterior 
ethmoidal  foramen 


Posterior  ethmoidal  foramen 
Orbital  process  of  palatine 
/  Optic  foramen 

Sphenopalatine  foramen 
Sella  turcica 
I  Probe  in  foramen  rot  undum 


Fossa  for 

lacrimal  sac 

Uncinate  process 
of  ethmoid 
Openings  of 
maxillary  sinus 
Inferior  nasal 
concha 


Probe  in  pterygoid  canal 
Probe  in  pterygopalatine  canal 

Palatine  bone 

Lateral  pterygoid  plate 


Pyramidal  process  cf  palatine 


Fig.   159. — Left  maxillary  sinus  opened  from  the  exterior. 


The  Maxillary  Sinus  or  Antrum  of  Highmore  {sinus  maxillaris). — The  maxillary 
sinus  is  a  large  pyramidal  cavity,  within  the  body  of  the  maxilla :  its  apex,  directed 
lateralward,  is  formed  by  the  zygomatic  process;  its  base,  directed  medialward, 
by  the  lateral  wall  of  the  nose.  Its  walls  are  everywhere  exceedingly  thin,  and 
correspond  to  the  nasal  orbital,  anterior,  and  infratemporal  surfaces  of  the  body 
of  the  bone.  Its  nasal  wall,  or  base,  presents,  in  the  disarticulated  bone,  a  large, 
irregular  aperture,  communicating  with  the  nasal  cavity.  In  the  articulated 
skull  this  aperture  is  much  reduced  in  size  by  the  following  bones:  the  uncinate 
process  of  the  ethmoid  above,  the  ethmoidal  process  of  the  inferior  nasal  concha 
below,  the  vertical  part  of  the  palatine  behind,  and  a  small  part  of  the  lacrimal 
above  and  in  front  (Figs.  158,  159) ;  the  sinus  communicates  with  the  middle  meatus 


THE  MAXILLA  161 

of  the  nose,  generally  by  two  small  apertures  left  between  the  above-mentioned 
bones.  In  the  fresh  state,  usually  only  one  small  opening  exists,  near  the  upper 
part  of  the  cavity;  the  other  is  closed  by  mucous  membrane.  On  the  posterior 
wall  are  the  alveolar  canals,  transmitting  the  posterior  superior  alveolar  vessels 
and  nerves  to  the  molar  teeth.  The  floor  is  formed  by  the  alveolar  process  of  the 
maxilla,  and,  if  the  sinus  be  of  an  average  size,  is  on  a  level  with  the  floor  of 
the  nose;  if  the  sinus  be  large  it  reaches  below  this  level. 

Projecting  into  the  floor  of  the  antrum  are  several  conical  processes,  correspond- 
ing to  the  roots  of  the  first  and  second  molar  teeth  ;^  in  some  cases  the  floor  is 
perforated  by  the  fangs  of  the  teeth.  The  infraorbital  canal  usually  projects  into 
the  cavity  as  a  well-marked  ridge  extending  from  the  roof  to  the  anterior  wall; 
additional  ridges  are  sometimes  seen  in  the  posterior  wall  of  the  cavity,  and 
are  caused  by  the  alveolar  canals.  The  size  of  the  cavity  varies  in  different  skulls, 
and  even  on  the  tw^o  sides  of  the  same  skull. ^ 

The  Zygomatic  Process  (processus  zygomaticus;  malar  process). — ^The  zygomatic 
process  is  a  rough  triangular  eminence,  situated  at  the  angle  of  separation  of  the 
anterior,  zygomatic,  and  orbital  surfaces.  In  front  it  forms  part  of  the  anterior 
surface;  behind,  it  is  concave,  and  forms  part  of  the  infratemporal  fossa;  above, 
it  is  rough  and  serrated  for  articulation  with  the  zygomatic  bone;  while  below, 
it  presents  the  prominent  arched  border  which  marks  the  division  between  the 
anterior  and  infratemporal  surfaces. 

The  Frontal  Process  (processus  frontalis;  nasal  process). — The  frontal  process 
is  a  strong  plate,  which  projects  upward,  medialward,  and  backward,  by  the  side 
of  the  nose,  forming  part  of  its  lateral  boundary.  Its  lateral  surface  is  smooth, 
continuous  with  the  anterior  surface  of  the  body,  and  gives  attachment  to  the 
C^uadratus  labii  superioris,  the  Orbicularis  oculi,  and  the  medial  palpebral  ligament. 
Its  medial  surface  forms  part  of  the  lateral  wall  of  the  nasal  cavity;  at  its  upper 
part  is  a  rough,  uneven  area,  which  articulates  with  the  ethmoid,  closing  in  the 
anterior  ethmoidal  cells;  below  this  is  an  oblique  ridge,  the  ethmoidal  crest,  the 
}iosterior  end  of  which  articulates  with  the  middle  nasal  concha,  while  the  anterior 
})art  is  termed  the  agger  nasi;  the  crest  forms  the  upper  limit  of  the  atrium  of  the 
middle  meatus.  The  upper  border  articulates  with  the  frontal  bone  and  the  anterior 
^vith  the  nasal;  the  posterior  border  is  thick,  and  hollowed  into  a  groove,  which  is 
continuous  below  with  the  lacrimal  groove  on  the  nasal  surface  of  the  body:  by 
ihe  articulatioji  of  the  medial  margin  of  the  groove  with  the  anterior  border  of 
ihe  lacrimal  a  corresponding  groove  on  the  lacrimal  is  brought  into  continuity, 
;md  together  they  form  the  lacrimal  fossa  for  the  lodgement  of  the  lacrimal  sac. 
The  lateral  margin  of  the  groove  is  named  the  anterior  lacrimal  crest,  and  is  con- 
linuous  below  with  the  orbital  margin;  at  its  junction  with  the  orbital  surface  is 
a  small  tubercle,  the  lacrimal  tubercle,  which  serves  as  sc  guide  to  the  position  of 
:he  lacrimal  sac. 

The  Alveolar  Process  (processus  alveolaris). — The  alveolar  process  is  the  thickest 
and  most  spongy  part  of  the  bone.  It  is  broader  behind  than  in  front,  and  exca- 
vated into  deep  cavities  for  the  reception  of  the  teeth.  These  cavities  are  eight 
n  number,  and  vary  in  size  and  depth  according  to  the  teeth  they  contain.  That 
:'or  the  canine  tooth  is  the  deepest;  those  for  the  molars  are  the  widest,  and  are 
subdivided  into  minor  cavities  by  septa;  those  for  the  incisors  are  single,  but 
deep  and  narrow.  The  Buccinator  arises  from  the  outer  surface  of  this  process, 
as  far  forward  as  the  first  molar  tooth.  When  the  maxillse  are  articulated  with  each 
other,  their  alveolar  processes  together  form  the  alveolar  arch;  the  center  of  the 
anterior  margin  of  this  arch  is  named  the  alveolar  point. 

'  The  number  of  teeth  whose  roots  are  in  relation  with  the  floor  of  the  antrum  is  variable.  The  sinus  "may  extend 
so  aa  to  be  in  relation  to  all  the  teeth  of  the  true  maxilla,  from  the  canine  to  the  dens  aapienliw. "  _  (Salter.) 

-  Aldren  Turner  (op.  cit.)  gives  the  following  measurements  as  those  of  an  average  sized  sinus:  vertical  height 
opposite  first  molar  tooth,  1}-^  inch;  transverse  breadth,  1  inch;  and  antero-posterior  depth,  \\i  inch. 


i 


11 


162 


OSTEOLOGY 


The  Palatine  Process  (processus  yalatinus;  palatal  process). — The  palatine 
process,  thick  and  strong,  is  horizontal  and  projects  medialward  from  the  nasal 
surface  of  the  bone.  It  forms  a  considerable  part  of  the  floor  of  the  nose  and  the 
roof  of  the  mouth  and  is  much  thicker  in  front  than  behind.  Its  inferior  surface 
(Fig.  160)  is  concave,  rough  and  uneven,  and  forms,  with  the  palatine  process  of 
the  opposite  bone,  the  anterior  three-fourths  of  the  hard  plate.  It  is  perforated 
by  numerous  foramina  for  the  passage  of  the  nutrient  vessels;  is  channelled  at  the 
back  part  of  its  lateral  border  by  a  groove,  sometimes  a  canal,  for  the  transmission 
of  the  descending  palatine  vessels  and  the  anterior  palatine  nerve  from  the  spheno- 
palatine ganglion;  and  presents  little  depressions  for  the  lodgement  of  the  palatine 
glands.  When  the  two  maxillae  are  articulated,  a  funnel-shaped  opening,  the 
incisive  foramen,  is  seen  in  the  middle  line,  immediately  behind  the  incisor  teeth. 
In  this  opening  the  orifices  of  two  lateral  canals  are  visible;  they  are  named  the 


Incisive  cavMs 


Incisive  foramen 


Foramina  of  Scarpa 


Palatine  process  of  maxilla  \        Greater  palatine  foramen 

Horizontal  plate  of  palatine  bone  Lesser  palatine  foramina 

Fig.   160. — The  bony  palate  and  alveolar  arch. 

incisive  canals  or  foramina  of  Stenson;  through  each  of  them  passes  the  terminal 
branch  of  the  descending  palatine  artery  and  the  nasopalatine  nerve.  Occasionally 
two  additional  canals  are  present  in  the  middle  line;  they  are  termed  the  foramina 
of  Scarpa,  and  when  present  transmit  the  nasopalatine  nerves,  the  left  passing 
through  the  anterior,  and  the  right  through  the  posterior  canal.  On  the  under 
surface  of  the  palatine  process,  a  delicate  linear  suture,  well  seen  in  young  skulls, 
may  sometimes  be  noticed  extending  lateralward  and  forward  on  either  side  from 
the  incisive  foramen  to  the  interval  between  the  lateral  incisor  and  the  canine  tooth. 
The  small  part  in  front  of  this  suture  constitutes  the  premaxilla  (os  incisivum), 
which  in  most  vertebrates  forms  an  independent  bone;  it  includes  the  whole  thick- 
ness of  the  alveolus,  the  corresponding  part  of  the  floor  of  the  nose  and  the  anterior 
nasal  spine,  and  contains  the  sockets  of  the  incisor  teeth.  The  upper  surface  of 
the  palatine  process  is  concave  from  side  to  side,  smooth,  and  forms  the  greater 
part  of  the  floor  of  the  nasal  cavity.    It  presents,  close  to  its  medial  margin,  the 


I 


THE  LACRIMAL  BONE 


163 


upper  orifice  of  the  incisive  canal.  The  lateral  border  of  the  process  is  incorporated 
with  the  rest  of  the  bone.  The  medial  border  is  thicker  in  front  than  behind,  and 
is  raised  above  into  a  ridge,  the  nasal  crest,  which,  with  the  corresponding  ridge 
of  the  opposite  bone,  forms  a  groove  for  the  reception  of  the  vomer.  The  front 
part  of  this  ridge  rises  to  a  considerable  height,  and  is  named  the  incisor  crest; 
it  is  prolonged  forw^ard  into  a  sharp  process,  which  forms,  together  wdth  a  similar 
process  of  the  opposite  bone,  the  anterior  nasal  spine.  The  posterior  border  is  ser- 
rated for  articulation  with  the  horizontal  part  of  the  palatine  bone. 

Ossification. — The  maxilla  is  ossified  in  membrane.  Mall^  and  Fawcett^  maintain  that  it  is 
ossified  from  two  centers  only,  one  for  the  maxilla  proper  and  one  for  the  premaxilla.  These 
centers  appear  dm-ing  the  sixth  week  of  fetal  life  and  unite  in  the  beginning  of  the  third  month, 
but  the  suture  between  the  two  portions  persists  on  the  palate  until  nearly  middle  life.  Mall 
states  that  the  frontal  process  is  developed  from  both  centers.  The  maxillary  sinus  appears  as 
a  shallow  groove  on  the  nasal  surface  of  the  bone  about  the  fourth  month  of  fetal  life,  but  does 
not  reach  its  full  size  xmtil  after  the  second  dentition.  The  maxilla  was  formerly  described  as 
ossifying  from  six  centers,  viz.,  one,  the  orbitonasal,  forms  that  portion  of  the  body  of  the  bone 
which  lies  medial  to  the  infraorbital  canal,  including  the  medial  part  of  the  floor  of  the  orbit  and 
the  lateral  wall  of  the  nasal  cavity;  a  second,  the  zygomatic,  gives  origin  to  the  portion  which  lies 
lateral  to  the  infraorbital  canal,  including  the  zygomatic  process;  from  a  third,  the  palatine,  is 
developed  the  palatine  process  posterior  to  the  incisive  canal  together  with  the  adjoining  part 
of  the  nasal  wall;  a  fourth,  the  premaxillary,  forms  the  incisive  bone  which  carries  the  incisor 


:g.  161. — Anterior  surface  of  maxilla  at  birth. 


Fig.   162. — Inferior  surface  of  maxilla  at  birth. 


I 


teeth  and  corresponds  to  the  premaxiUa  of  the  lower  vertebrates;'  a  fifth,  the  nasal,  gives  rise  to 
lhe  frontal  process  and  the  portion  above  the  canine  tooth;  and  a  sixth,  the  infravomerine,  lies 
between  the  palatine  and  premaxillary  centers  and  beneath  the  vomer;  this  center,  together  with 
i,he  corresponding  center  of  the  opposite  bone,  separates  the  incisive  canals  from  each  other. 

Articulations. — The  maxilla  articulates  with  nine  bones:  two  of  the  cranium,  the  frontal  and 
ithmoid,  and  seven  of  the  face,  viz.,  the  nasal,  zygomatic,  lacrimal,  inferior  nasal  concha,  palatine, 
/omer,  and  its  fellow  of  the  opposite  side.  Sometimes  it  articulates  with  the  orbital  surface, 
md  sometimes  with  the  lateral  pterygoid  plate  of  the  sphenoid. 

r  CHANGES   PRODUCED   IN   THE    MAXILLA   BY   AGE. 

At  birth  the  transverse  and  antero-posterior  diameters  of  the  bone  are  each  greater  than  the 
vertical.  The  frontal  process  is  well-marked  and  the  body  of  the  bone  consists  of  little  more  than 
the  alveolar  process,  the  teeth  sockets  reaching  almost  to  the  floor  of  the  orbit.  The  maxillary 
sinus  presents  the  appearance  of  a  furrow  on  the  lateral  wall  of  the  nose.  In  the  adult  the  vertical 
diameter  is  the  greatest,  owing  to  the  development  of  the  alveolar  process  and  the  increase  in 
size  of  the  sinus.  In  old  age  the  bone  reverts  in  some  measure  to  the  infantile  condition;  its 
height  is  diminished,  and  after  the  loss  of  the  teeth  the  alveolar  process  is  absorbed,  and  the 
lower  part  of  the  bone  contracted  and  reduced  in  thickness. 

If  The  lacrimal  bone,  the  smallest  and  most  fragile  bone  of  the  face,  is  situated 
at  the  front  part  of  the  medial  wall  of  the  orbit  (Fig.  164).  It  has  two  surfaces 
and  four  borders. 

1  American  Journal  of  Anatomy,  1906,  vol.  v. 

2  Journal  of  Anatomy  and  Physiology,  1911,  vol.  xlv. 
'  Some  anatomists  believe  that  the  premaxillary  bone  is  ossified  by  two  centers  (see  page  299). 


The  Lacrimal  Bone  (Os  Lacrimale). 


164 


I 


tWM  Fron/til 


With 
Injer.  nasal  concha 
Fig.  163. — Left  lacri- 
mal bone.    Orbital  sur- 
face.   Enlarged. 


Surfaces. — The  lateral  or  orbital  surface  (Fig.  163)  is  divided  by  a  vertical  ridge, 
the  posterior  lacrimal  crest,  into  two  parts.  In  front  of  this  crest  is  a  longitudinal 
groove,  the  lacrimal  sulcus  (sulcus  lacrimalis),  the  inner  margin  of  which  unites 
with  the  frontal  process  of  the  maxilla,  and  the  lacrimal  fossa  is  thus  completed. 
The  upper  part  of  this  fossa  lodges  the  lacrimal  sac,  the  lower  part,  the  naso- 
lacrimal duct.  The  portion  behind  the  crest  is  smooth,  and  forms  part  of  the 
medial  wall  of  the  orbit.  The  crest,  with  a  part  of  the  orbital  surface  imme- 
diately behind  it,  gives  origin  to  the  lacrimal  part  of  the  Orbicularis  oculi  and 
ends  below  in  a  small,  hook-like  projection,  the  lacrimal  hamulus,  which  articu- 
lates with  the  lacrimal  tubercle  of  the  maxilla,  and  completes 
the  upper  orifice  of  the  lacrimal  canal;  it  sometimes  exists  as 
a  separate  piece,  and  is  then  called  the  lesser  lacrimal  bone. 

The  medial  or  nasal  surface  presents  a  longitudinal  furrow, 
corresponding  to  the  crest  on  the  lateral  surface.  The  area  in 
front  of  this  furrow  forms  part  of  the  middle  meatus  of  the 
nose;  that  behind  it  articulates  with  the  ethmoid,  and  completes 
some  of  the  anterior  ethmoidal  cells. 

Borders. — Of  the  four  borders  the  anterior  articulates  with 
the  frontal  process  of  the  maxilla;  the  posterior  with  the  lamina 
papyracea  of  the  ethmoid;  the  superior  with  the  frontal  bone. 
The  inferior  is  divided  by  the  lower  edge  of  the  posterior  lacri- 
mal crest  into  two  parts :  the  posterior  part  articulates  with  the 
orbital  plate  of  the  maxilla;  the  anterior  is  prolonged  downward 
as  the  descending  process,  which  articulates  with  the  lacrimal  process  of  the  inferior 
nasal  concha,  and  assists  in  forming  the  canal  for  the  nasolacrimal  duct. 

Ossification. — The  lacrimal  is  ossified  from  a  single  center,  which  appears  about  the  twelfth 
week  in  the  membrane  covering  the  cartilaginous  nasal  capsule. 

Articulations. — The  lacrimal  articulates  with  four  bones:  two  of  the  cranium,  the  frontal 
and  ethmoid,  and  two  of  the  face,  the  maxilla  and  the  inferior  nasal  concha. 

The  Zygomatic  Bone  (Os  Zygomaticum ;  Malar  Bone). 

The  zygomatic  bone  is  small  and  quadrangular,  and  is  situated  at  the  upper 
and  lateral  part  of  the  face:  it  forms  the  prominence  of  the  cheek,  part  of  the 
lateral  wall  and  floor  of  the  orbit,  and  parts  of  the  temporal  and  infratemporal 
fossae  (Fig.  164).  It  presents  a  malar  and  a  temporal  surface;  four  processes,  the 
frontosphenoidal,  orbital,  maxillary,  and  temporal;  and  four  borders. 

Surfaces. — The  malar  surface  (Fig.  165)  is  convex  and  perforated  near  its  center 
by  a  small  aperture,  the  zygomaticofacial  foramen,  for  the  passage  of  the  zygomatico- 
facial nerve  and  vessels;  below  this  foramen  is  a  slight  elevation,  which  gives 
origin  to  the  Zygomaticus. 

The  temporal  surface  (Fig.  166),  directed  backward  and  medialward,  is  concave, 
presenting  medially  a  rough,  triangular  area,  for  articulation  with  the  maxilla, 
and  laterally  a  smooth,  concave  surface,  the  upper  part  of  which  forms  the  anterior 
boundary  of  the  temporal  fossa,  the  lower  a  part  of  the  infratemporal  fossa.  Near 
the  center  of  this  surface  is  the  zygomaticotemporal  foramen  for  the  transmission 
of  the  zygomaticotemporal  nerve. 

Processes. — The  frontosphenoidal  process  is  thick  and  serrated,  and  articulates 
with  the  zygomatic  process  of  the  frontal  bone.  On  its  orbital  surface,  just  within 
the  orbital  margin  and  about  11  mm.  below  the  zygomaticofrontal  suture  is  a 
tubercle  of  varying  size  and  form,  but  present  in  95  per  cent,  of  skulls  (WhitnalP). 

'  Journal  of  Anatomy  and  Physiology,  vol.  xlv.  The  structures  attached  to  this  tubercle  are:  (1)  the  check 
ligament  of  the  Rectus  lateralis;  (2)  the  lateral  end  of  the  aponeurosis  of  the  Levator  palpebrse  superioris;  (3)  the 
suspensory  ligament  of  the  eye  (Lookwood);  and  (4)  the  lateral  extremities  of  the  superior  and  inferior  tarsi. 


THE  ZYGOMATIC  BONE 


165 


The  orbital  process  is  a  thick,  strong  plate,  projecting  backward  and  medialward 
from  the  orbital  margin.  Its  antero-medial  surface  forms,  by  its  junction  with 
the  orbital  surface  of  the  maxilla  and  with  the  great  wing  of  the  sphenoid,  part 
of  the  floor  and  lateral  wall  of  the  orbit.    On  it  are  seen  the  orifices  of  two  canals, 


Pa  7~{eta1 


Fig.   164 — Left  zygomatic  bone  in  situ. 


the  zygomaticoorbital  foramina;  one  of  these  canals  opens  into  the  temporal  fossa, 
the  other  on  the  malar  surface  of  the  bone;  the  former  transmits  the  zygomatico- 
temporal, the  latter  the  zygomaticofacial  nerve.  Its  postero-lateral  surface,  smooth 
fcsnd  convex,  forms  parts  of  the  temporal  and  infratemporal  fossae.  Its  anterior 
margin,  smooth  and  rounded,  is  part  of  the  circumference  of  the  orbit.    Its  superior 


With  Frontal 


^iristles  passed 
through 
_   zygomatico-        /i 
orbital  foramina  J  a 


Fig.   106. — Left  zygomatic  bone.     Temporal  surface. 


margin,  rough,  and  directed  horizontally,  articulates  with  the  frontal  bone  behind 
xhe  zygomatic  process.  Its  posterior  margin  is  serrated  for  articulation,  with  the 
great  wing  of  the  sphenoid  and  the  orbital  surface  of  the  maxilla.  At  the  angle 
of  junction  of  the  sphenoidal  and  maxillary  portions,  a  short,  concave,  non-articular 


166 


OSTEOLOGY 


I 


part  is  generally  seen;  this  forms  the  anterior  boundary  of  the  inferior  orbital  fissure: 
occasionally,  this  non-articular  part  is  absent,  the  fissure  then  being  completed 
by  the  junction  of  the  maxilla  and  sphenoid,  or  by  the  interposition  of  a  small 
sutural  bone  in  the  angular  interval  between  them.  The  maxillary  process  presents 
a  rough,  triangular  surface  which  articulates  with  the  maxilla.  The  temporal 
process,  long,  narrow,  and  serrated,  articulates  with  the  zygomatic  process  of  the 
temporal. 

Borders. — The  antero-superior  or  orbital  border  is  smooth,  concave,  and  forms 
a  considerable  part  of  the  circumference  of  the  orbit.  The  antero-inferior  or  maxil- 
lary border  is  rough,  and  bevelled  at  the  expense  of  its  inner  table,  to  articulate 
with  the  maxilla;  near  the  orbital  margin  it  gives  origin  to  the  Quadratus  labii 
superioris.  The  postero-superior  or  temporal  border,  curved  like  an  italic  letter  /, 
is  continuous  above  with  the  commencement  of  the  temporal  line,  and  below  with 
the  upper  border  of  the  zygomatic  arch;  the  temporal  fascia  is  attached  to  it. 
The  postero-inferior  or  zygomatic  border  affords  attachment  by  its  rough  edge  to 
the  Masseter. 

Ossification. — The  zygomatic  bone  is  generally  described  as  ossifying  from  three  centers — 
one  for  the  malar  and  two  for  the  orbital  portion;  these  appear  about  the  eighth  week  and  fuse 
about  the  fifth  month  of  fetal  life.  Mall  describes  it  as  being  ossified  from  one  center  which 
appears  just  beneath  and  to  the  lateral  side  of  the  orbit.  After  birth,  the  bone  is  sometimes 
divided  by  a  horizontal  suture  into  an  upper  larger,  and  a  lower  smaller  division.  In  some  quad- 
rumana  the  zygomatic  bone  consists  of  two  parts,  an  orbital  and  a  malar. 

Articulations. — The  zygomatic  articulates  with  four  bones :  the  frontal,  sphenoidal,  temporal, 
and  maxilla. 


Groove  for 
nasolacrimal  duct 


Frontal  process 


Maxillary  sinus 
Orbital  process 


Sphenopalatine 
notch 

Sphenoidal 
process 


Conciial  crest. 


Conchal  crest 


Fio.  167. — Articulation  of  left  palatine  bone  with  maxilla. 

The  Palatine  Bone  (Os  Palatinum;  Palate  Bone). 

The  palatine  bone  is  situated  at  the  back  part  of  the  nasal  cavity  between  the 
maxilla  and  the  pterygoid  process  of  the  sphenoid  (Fig.  167).  It  contributes 
to  the  walls  of  three  cavities:  the  floor  and  lateral  wall  of  the  nasal  cavity,  the 
roof  of  the  mouth,  and  the  floor  of  the  orbit;  it  enters  into  the  formation  of  two 
fossae,  the  pterygopalatine  and  pterygoid  fossae;  and  one  fissure,  the  inferior  orbital 
fissure.  The  palatine  bone  somewhat  resembles  the  letter  L,  and  consists  of  a 
horizontal  and  a  vertical  part  and  three  outstanding  processes — viz.,  the  pyramidal 


THE  PALATINE  BONE 


167 


process,  which  is  directed  backward  and  lateralward  from  the  junction  of  the  two 
parts,  and  the  orbital  and  sphenoidal  processes,  which  surmount  the  vertical 
part,  and  are  separated  by  a  deep  notch,  the  sphenopalatine  notch. 

The  Horizontal  Part  {yars  horizontalis;  horizontal  plate)  (Figs.  168,  169). — The 
horizontal  part  is  quadrilateral,  and  has  two  surfaces  and  four  borders. 

Surfaces. — The  superior  surface,  concave  from  side  to  side,  forms  the  back  part 
of  the  floor  of  the  nasal  cavity.  The  inferior  surface,  slightly  concave  and  rough, 
forms,  with  the  corresponding  surface  of  the  opposite  bone,  the  posterior  fourth 
of  the  hard  palate.  Near  its  posterior  margin  may  be  seen  a  more  or  less  marked 
transverse  ridge  for  the  attachment  of  part  of  the  aponeurosis  of  the  Tensor  veli 
palatini. 


iiCtl  Bl\ 


Maxillary  surface 


Superior  meatus 
Sphenopalatine  foramen 


Sphenopalatine, 
forarrten 

Sphenoidal  process 
Articular  portion 


Posterior 
nasal 
Musevdus  uvulee  spine 


HORIZONTAL  PARI? 

168. — Left  palatine  bone. 
Enlarged. 


Pyramidal 
process 


HORIZONTAL 
PART 


Nasal  aspect. 


Fig.   169.- 


-Left  palatine  bone. 
Enlarged. 


Posterior  aspect. 


Maxillary 
process 


w 

^1  Borders. — The  anterior  border  is  serrated,  and  articulates  with  the  palatine  process 
''  cf  the  maxilla.  The  posterior  border  is  concave,  free,  and  serves  for  the  attachment 
(i  the  soft  palate.  Its  medial  end  is  sharp  and  pointed,  and,  when  united  with 
that  of  the  opposite  bone,  forms  a  projecting  process,  the  posterior  nasal  spine 
lor  the  attachment  of  the  Musculus  uvulae.  The  lateral  border  is  united  with 
the  lower  margin  of  the  perpendicular  part,  and  is  grooved  by  the  lower  end  of 
Ihe  pterygopalatine  canal.  The  medial  border,  the  thickest,  is  serrated  for  articu- 
lation with  its  fellow  of  the  opposite  side;  its  superior  edge  is  raised  into  a  ridge, 
Avhich,  united  with  the  ridge  of  the  opposite  bone,  forms  the  nasal  crest  for  articu- 
lation with  the  posterior  part  of  the  lower  edge  of  the  vomer. 

The  Vertical  Part  {yars  perpendicularis;  perpendicular  plate)  (Figs.  168,  169). — 
The  vertical  part  is  thin,  of  an  oblong  form,  and  presents  two  surfaces  and  four 
^H)>orders. 

H  _  Surfaces. — The  nasal  surface  exhibits  at  its  lower  part  a  broad,  shallow  depres- 
^sion,  which  forms  part  of  the  inferior  meatus  of  the  nose.  Immediately  above  this 
is  a  well-marked  horizontal  ridge,  the  conchal  crest,  for  articulation  with  the 
inferior  nasal  concha;  still  higher  is  a  second  broad,  shallow  depression,  which 
forms  part  of  the  middle  meatus,  and  is  limited  above  by  a  horizontal  crest  less 
prominent  than  the  inferior,  the  ethmoidal  crest,  for  articulation  with  the  middle 
nasal  concha.  Above  the  ethmoidal  crest  is  a  narrow,  horizontal  groove,  which 
forms  part  of  the  superior  meatus. 


i 


168 


OSTEOLOGY 


The  maxillary  surface  is  rough  and  irregular  throughout  the  greater  parTo 
extent,  for  articulation  with  the  nasal  surface  of  the  maxilla;  its  upper  and  back 
part  is  smooth  where  it  enters  into  the  formation  of  the  pterygopalatine  fossa; 
it  is  also  smooth  in  front,  where  it  forms  the  posterior  part  of  the  medial  A^all 
of  the  maxillary  sinus.  On  the  posterior  part  of  this  surface  is  a  deep  vertical 
groove,  converted  into  the  pterygopalatine  canal,  by  articulation  with  the  maxilla; 
this  canal  transmits  the  descending  palatine  vessels,  and  the  anterior  palatine 
nerve. 

Borders. — The  anterior  border  is  thin  and  irregular;  opposite  the  conchal  crest  is  a 
pointed,  projecting  lamina,  the  maxillary  process,  which  is  directed  forward,  and 
closes  in  the  lower  and  back  part  of  the  opening  of  the  maxillary  sinus.  The 
posterior  border  (Fig.  169)  presents  a  deep  groove,  the  edges  of  which  are  serrated 
for  articulation  with  the  medial  pterygoid  plate  of  the  sphenoid.  This  border 
is  continuous  above  with  the  sphenoidal  process;  below  it  expands  into  the 
pyramidal  process.  The  superior  border  supports  the  orbital  process  in  front  and  the 
sphenoidal  process  behind.  These  processes  are  separated  by  the  sphenopalatine 
notch,  which  is  converted  into  the  sphenopalatine  foramen  by  the  under  surface  of 
the  body  of  the  sphenoid.  In  the  articulated  skull  this  foramen  leads  from  the 
pterygopalatine  fossa  into  the  posterior  part  of  the  superior  meatus  of  the  nose, 
and  transmits  the  sphenopalatine  vessels  and  the  superior  nasal  and  nasopalatine 
nerves.  The  inferior  border  is  fused  with  the  lateral  edge  of  the  horizontal  part, 
and  immediately  in  front  of  the  pyramidal  process  is  grooved  by  the  lower  end 
of  the  pterygopalatine  canal. 

The  Pyramidal  Process  or  Tuberosity  (processus  pyrmnidalis) . — The  pyramidal 
process  projects  backward  and  lateralward  from  the  junction  of  the  horizontal 
and  vertical  parts,  and  is  received  into  the  angular  interval  between  the  lower 
extremities  of  the  pterygoid  plates.  On  its  posterior  surface  is  a  smooth,  grooved, 
triangular  area,  limited  on  either  side  by  a  rough  articular  furrow.  The  furrows 
articulate  with  the  pterygoid  plates,  while  the  grooved  intermediate  area  completes 
the  lower  part  of  the  pterygoid  fossa  and  gives  origin  to  a  few  fibers  of  the  Ptery- 
goideus  internus.  The  anterior  part  of  the  lateral  surface  is  rough,  for  articulation 
with  the  tuberosity  of  the  maxilla;  its  posterior  part  consists  of  a  smooth  triangular 
area  which  appears,  in  the  articulated  skull,  beWeen  the  tuberosity  of  the  maxilla 
and  the  lower  part  of  the  lateral  pterygoid  plate,  and  completes  the  lower  part 
of  the  infratemporal  fossa.  On  the  base  of  the  pyramidal  process,  close  to  its 
union  with  the  horizontal  part,  are  the  lesser  palatine  foramina  for  the  transmis- 
sion of  the  posterior  and  middle  palatine  nerves. 

The  Orbital  Process  (processus  orbitalis). — The  orbital  process  is  placed  on  a 
higher  level  than  the  sphenoidal,  and  is  directed  upward  and  lateralward  from 
the  front  of  the  vertical  part,  to  which  it  is  connected  by  a  constricted  neck.  It 
presents  five  surfaces,  which  enclose  an  air  cell.  Of  these  surfaces,  three  are  articu- 
lar and  two  non-articular.  The  articular  surfaces  are:  (1)  the  anterior  or  maxillary, 
directed  forward,  lateralward,  and  downward,  of  an  oblong  form,  and  rough  for 
articulation  with  the  maxilla;  (2)  the  posterior  or  sphenoidal,  directed  backward, 
upward,  and  medialward;  it  presents  the  opening  of  the  air  cell,  w^hich  usually 
communicates  with  the  sphenoidal  sinus;  the  margins  of  the  opening  are  serrated 
for  articulation  with  the  sphenoidal  concha;  (3)  the  medial  or  ethmoidal,  directed 
forward,  articulates  with  the  labyrinth  of  the  ethmoid.  In  some  cases  the  air 
cell  opens  on  this  surface  of  the  bone  and  then  communicates  with  the  posterior 
ethmoidal  cells.  ]More  rarely  it  opens  on  both  surfaces,  and  then  communicates 
with  the  posterior  ethmoidal  cells  and  the  sphenoidal  sinus.  The  non-articular 
surfaces  are:  (1)  the  superior  or  orbital,  directed  upward  and  lateralward;  it  is 
triangular  in  shape,  and  forms  the  back  part  of  the  floor  of  the  orbit;  and  (2)  the 
lateral,  of  an  oblong  form,  directed  toward  the  pterygopalatine  fossa;  it  is  separated 


THE  INFERIOR  NASAL  CONCHA  169 

from  the  orbital  surface  by  a  rounded  border,  which  enters  into  the  formation  of 
the  inferior  orbital  fissure. 

The  Sphenoidal  Process  {processus  sphenoidalis) . — The  sphenoidal  process  is 
a  thin,  compressed  plate,  much  smaller  than  the  orbital,  and  directed  upward 
and  mediahvard.  It  presents  three  surfaces  and  two  borders.  The  superior  surface 
articulates  with  the  root  of  the  pterygoid  process  and  the  under  surface  of  the 
sphenoidal  concha,  its  medial  border  reaching  as  far  as  the  ala  of  the  vomer;  it 
presents  a  groove  which  contributes  to  the  formation  of  the  pharyngeal  canal. 
The  medial  surface  is  concave,  and  forms  part  of  the  lateral  wall  of  the  nasal  cavity. 
The  lateral  surface  is  divided  into  an  articular  and  a  non-articular  portion:  the 
former  is  rough,  for  articulation  with  the  medial  pterygoid  plate;  the  latter  is 
smooth,  and  forms  part  of  the  pterygopalatine  fossa.  The  anterior  border  forms 
the  posterior  boundary  of  the  sphenopalatine  notch.  The  posterior  border,  ser- 
rated at  the  expense  of  the  outer  table,  articulates  with  the  medial  pterygoid 
plate. 

The  orbital  and  sphenoidal  processes  are  separated  from  one  another  by  the 
sphenopalatine  notch.  Sometimes  the  two  processes  are  united  above,  and  form 
between  them  a  complete  foramen  (Fig.  168),  or  the  notch  may  be  crossed  by  one 
or  more  spicules  of  bone,  giving  rise  to  two  or  more  foramina. 

Ossification. — The  palatine  bone  is  ossified  in  membrane  from  a  single  center,  which  makes 
its  appearance  about  the  sixth  or  eighth  week  of  fetal  life  at  the  angle  of  junction  of  the  two  parts 
O"  the  bone.  From  this  point  ossification  spreads  medialward  to  the  horizontal  part,  downward 
into  the  pyramidal  process,  and  upward  into  the  vertical  part.  Some  authorities  describe  the 
bone  as  ossifying  from  four  centers:  one  for  the  pyramidal  process  and  portion  of  the  vertical 
part  behind  the  pterygopalatine  groove;  a  second  for  the  rest  of  the  vertical  and  the  horizontal 
parts;  a  third  for  the  orbital,  and  a  fourth  for  the  sphenoidal  process.  At  the  time  of  birth  the 
height  of  the  vertical  part  is  about  equal  to  the  transverse  width  of  the  horizontal  part,  whereas 
ill  the  adult  the  former  measures  about  twice  as  much  as  the  latter. 

Artictllations. — The  palatine  articulates  with  six  bones:  the  sphenoid,  ethmoid,  maxilla, 
inferior  nasal  concha,  vomer,  and  opposite  palatine. 

"|i 

fthe  Inferior  Nasal  Concha  (Concha  Nasalis  Inferior;  Inferior  Turbinated  Bone). 

The  inferior  nasal  concha  extends  horizontally  along  the  lateral  wall  of  the 
lasal  cavity  (Fig.  170)  and  consists  of  a  lamina  of  spongy  bone,  curled  upon  itself 
ike  a  scroll.    It  has  two  surfaces,  two  borders,  and  two  extremities. 

The  medial  surface  (Fig.  171)  is  convex,  perforated  by  numerous  apertures, 
jid  traversed  by  longitudinal  grooves  for  the  lodgement  of  vessels.  The  lateral 
nrface  is  concave  (Fig.  172),  and  forms  part  of  the  inferior  meatus.  Its  upper 
lorder  is  thin,  irregular,  and  connected  to  various  bones  along  the  lateral  wall 
>f  the  nasal  cavity.  It  may  be  divided  into  three  portions:  of  these,  the  anterior 
urticulates  with  the  conchal  crest  of  the  maxilla;  the  posterior  with  the  conchal 
rest  of  the  palatine;  the  middle  portion  presents  three  well-marked  processes, 
ihich  vary  much  in  their  size  and  form.  Of  these,  the  anterior  or  lacrimal  process 
k  small  and  pointed  and  is  situated  at  the  junction  of  the  anterior  fourth  with 
ihe  posterior  three-fourths  of  the  bone:  it  articulates,  by  its  apex,  with  the  descend- 
ing process  of  the  lacrimal  bone,  and,  by  its  margins,  with  the  groove  on  the  back 
of  the  frontal  process  of  the  maxilla,  and  thus  assists  in  forming  the  canal  for  the 
nasolacrimal  duct.  Behind  this  process  a  broad,  thin  plate,  the  ethmoidal  process, 
ascends  to  join  the  uncinate  process  of  the  ethmoid;  from  its  lower  border  a  thin 
lamina,  the  maxillary  process,  curves  downward  and  lateralward;  it  articulates 
'.vith  the  maxilla  and  forms  a  part  of  the  medial  wall  of  the  maxillary  sinus.  The 
inferior  border  is  free,  thick,  and  cellular  in  structure,  more  especially  in  the  middle 
of  the  bone.  Both  extremities  are  more  or  less  pointed,  the  posterior  being  the 
ore  tapering. 


I 


170 


OSTEOLOGY 


1 


Ossification. — The  inferior  nasal  concha  is  ossified  from  a  single  center,  which  appears' alout 
the  fifth  month  of  fetal  life  in  the  lateral  wall  of  the  cartilaginous  nasal  capsule. 

Articulations. — The  inferior  nasal  concha  articulates  with  four  bones:  the  ethmoid,  maxilla, 
lacrimal,  and  palatine. 


.  Uncinate 

process 
oj  ethmoid 


Openings  into 
maxillary  sinus 
Medial  pterygoid  plate 
Pterygoid  hamulus 


Fig.  170. — Lateral  wall  of  right  naaal  cavity  showing  inferior  concha  in  situ. 
.1- 


Fig.  171. — Right  inferior  nasal  concha. 
Medial  surface. 


Fig.  172. — Right  inferior  nasal  concha. 
Lateral  surface. 


The  Vomer. 

The  vomer  is  situated  in  the  median  plane,  but  its  anterior  portion  is  frequently 
bent  to  one  or  other  side.  It  is  thin,  somewhat  quadrilateral  in  shape,  and  forms 
the  hinder  and  lower  part  of  the  nasal  septum  (Fig.  173) ;  it  has  two  surfaces  and 
four  borders.  The  surfaces  (Fig.  174)  are  marked  by  small  furrows  for  blood- 
vessels, and  on  each  is  the  nasopalatine  groove,  which  runs  obliquely  downward 
and  forward,  and  lodges  the  nasopalatine  nerve  and  vessels.  The  superior  border, 
the  thickest,  presents  a  deep  furrow,  bounded  on  either  side  by  a  horizontal  pro- 
jecting ala  of  bone;  the  furrow  receives  the  rostrum  of  the  sphenoid,  while  the 
margins  of  the  alse  articulate  with  the  vaginal  processes  of  the  medial  pterygoid 
plates  of  the  sphenoid  behind,  and  with  the  sphenoidal  processes  of  the  palatine 
bones  in  front.    The  inferior  border  articulates  with  the  crest  formed  by  the  maxillae 


THE  VOMER 


171 


and  palatine  bones.  The  anterior  border  is  the  longest  and  slopes  downward  and 
forward.  Its  upper  half  is  fused  with  the  perpendicular  plate  of  the  ethmoid; 
its  lower  half  is  grooved  for  the  inferior  margin  of  the  septal  cartilage  of  the  nose. 
The  posterior  border  is  free,  concave,  and  separates  the  choanse.  It  is  thick  and 
bifid  above,  thin  below. 


Rostrum  of  sphenoid 


Crest  of  nasal  hones 
Frontal  spine 


Space  for  triangular 
cartilage  of  septum 


Crest  of  palatines 
Crest  of  maxiUoe 


Fig.  173. — Median  wall  of  left  nasal  cavity  showing  vomer  in  situ. 

Ossification. — At  an  early  period  the  septum  of  the  nose  consists  of  a  plate  of  cartilage,  the 
iQimovomerine  cartilage.  The  postero-superior  part  of  this  cartilage  is  ossified  to  form  the  per-, 
[endicular  plate  of  the  ethmoid;  its  antero-inferior  portion  persists  as  the  septal  cartilage,  while 
the  vomer  is  ossified  in  the  membrane  covering  its  postero-inferior  part.  Two  ossific  centers, 
one  on  either  side  of  the  middle  Une,  appear  about  the  eighth  week  of  fetal  life  in  this  part  of 
llhe  membrane,  and  hence  the  vomer  consists  primarily  of  two  lamellae.    About  the  third  month 


174. — The  vomer. 


Fig    175. — Vomer  of  infant. 


these  unite  below,  and  thus  a  deep  groove  is  formed  in  which  the  cartilage  is  lodged.  As 
:^owth  proceeds,  the  union  of  the  lamellae  extends  upward  and  forward,  and  at  the  same  time  the 
intervening  plate  of  cartilage  undergoes  absorption.  By  the  age  of  puberty  the  lamelte  are  almost 
completely  united  to  form  a  median  plate,  but  evidence  of  the  bilaminar  origin  of  the  bone  is 

Iaeen  in  the  everted  alae  of  its  upper  border  and  the  groove  on  its  anterior  margin. 
I 


172 


OSTEOLOGY 


I 


Articulations. — The  vomer  articulates  with  six  bones:  two  of  the  cranium,  the  sphenoid  and 
ethmoid;  and  four  of  the  face,  the  two  maxillaj  and  the  two  palatine  bones;  it  also  articuUtes 
with  the  septal  cartilage  of  the  nose. 


The  Mandible  (Mandibula ;  Inferior  Maxillary  Bone;  Lower  Jaw). 

The  mandible,  the  largest  and  strongest  bone  of  the  face,  serves  for  the  reception 
of  the  lower  teeth.  It  consists  of  a  curved,  horizontal  portion,  the  body,  and  two 
perpendicular  portions,  the  rami,  which  unite  with  the  ends  of  the  body  nearly 
at  right  angles. 

The  Body  {corpus  mandibuloe) . — The  body  is  curved  somewhat  like  a  horseshoe, 
and  has  two  surfaces  and  two  borders. 

Surfaces. — The  external  surface  (Fig.  176)  is  marked  in  the  median  line  by  a 
faint  ridge,  indicating  the  symphysis  or  line  of  junction  of  the  two  pieces  of  which 
the  bone  is  composed  at  an  early  period  of  life.  This  ridge  divides  below  and 
encloses  a  triangular  eminence,  the  mental  protuberance,  the  base  of  which  is  de- 


Goronoid  process 


Condyle 


TEMPORALIS 


""■■"li'KllUl///'    jif'  V 

^^"      Body  ^^^f" 
^^ntal        m^       "^^y-  ■  ..^^^^^-^^ 
protvherance-W^^^^^^^':^' J 


Qrocme.  for  external 
maxillary  artery 

Fig.   176. — Mandible.     Outer  surface.     Side  view. 


Am.  ale 


pressed  in  the  center  but  raised  on  either  side  to  form  the  mental  tubercle.  On  either 
side  of  the  symphysis,  just  below  the  incisor  teeth,  is  a  depression,  the  incisive 
fossa,  which  gives  origin  to  the  Mentalis  and  a  small  portion  of  the  Orbicularis 
oris.  Below  the  second  premolar  tooth,  on  either  side,  midway  between  the  upper 
and  lower  borders  of  the  body,  is  the  mental  foramen,  for  the  passage  of  the  mental 
vessels  and  nerve.  Running  backward  and  upward  from  each  mental  tubercle 
is  a  faint  ridge,  the  oblique  line,  which  is  continuous  with  the  anterior  border  of  the 
ramus;  it  affords  attachment  to  the  Quadratus  labii  inferioris  and  Triangularis; 
the  Platysma  is  attached  below  it. 

The  internal  surface  (Fig.  177)  is  concave  from  side  to  side.  Near  the  lower 
part  of  the  symphysis  is  a  pair  of  laterally  placed  spines,  termed  the  mental  spines, 
which  give  origin  to  the  Genioglossi.  Immediately  below  these  is  a  second  pair 
of  spines,  or  more  frequently  a  median  ridge  or  impression,  for  the  origin  of  the 
Geniohyoidei.  In  some  cases  the  mental  spines  are  fused  to  form  a  single  eminence, 
in  others  they  are  absent  and  their  position  is  indicated  merely  by  an  irregularity 
of  the  surface.  Above  the  mental  spines  a  median  foramen  and  furrow  are  some- 
times seen;  they  mark  the  line  of  union  of  the  halves  of  the  bone.    Below  the  mental 


THE  MANDIBLE 


173 


spines,  on  either  side  of  the  middle  line,  is  an  oval  depression  for  the  attachment 
of  the  anterior  belly  of  the  Digastricus.  Extending  upward  and  backward  on  either 
side  from  the  lower  part  of  the  symphysis  is  the  mylohyoid  line,  which  gives  origin 
to  the  Mylohyoideus ;  the  posterior  part  of  this  line,  near  the  alveolar  margin, 
gives  attachment  to  a  small  part  of  the  Constrictor  pharyngis  superior,  and  to 
the  pterygomandibular  raphe.  Above  the  anterior  part  of  this  line  is  a  smooth 
triangular  area  against  which  the  sublingual  gland  rests,  and  below  the  hinder 
part,  an  oval  fossa  for  the  submaxillary  gland. 

Borders. — The  superior  or  alveolar  border,  wider  behind  than  in  front,  is  hollowed 
into  cavities,  for  the  reception  of  the  teeth;  these  cavities  are  sixteen  in  number, 
and  vary  in  depth  and  size  according  to  the  teeth  which  they  contain.  To  the 
outer  lip  of  the  superior  border,  on  either  side,  the  Buccinator  is  attached  as 
far  forward  as  the  first  molar  tooth.  The  inferior  border  is  rounded,  longer  than 
the  superior,  and  thicker  in  front  than  behind;  at  the  point  where  it  joins  the 
lower  border  of  the  ramus  a  shallow  groove;  for  the  external  maxillary  artery, 
may  be  present. 


..,|1v  '^'^■"'/'o. 


Oenio- 

glossus 
Genio- 

hyoideus 


Mylohyoid  line 

BODY 
Fig.   177. — Mandible.     Inner  surface.     Side  view. 

\ 


The  Ramus  {ramus  mandibulcp;  perpeiidicular  portion). — The  ramus  is  quadri- 
lateral in  shape,  and  has  two  surfaces,  four  borders,  and  two  processes. 

Surfaces.^ — The  lateral  surface  (Fig.  176)  is  flat  and  marked  by  oblique  ridges 
at  its  lower  part;  it  gives  attachment  throughout  nearly  the  whole  of  its  extent 
tc  the  Masseter.  The  medial  surface  (Fig.  177)  presents  about  its  center  the  oblique 
mandibular  foramen,  for  the  entrance  of  the  inferior  alveolar  vessels  and  nerve. 
The  margin  qf  this  opening  is  irregular;  it  presents  in  front  a  prominent  ridge, 
surmounted  by  a  sharp  spine,  the  lin6:ula  mandibulae,  which  gives  attachment  to 
the  sphenomandibular  ligament ;  at  its  lower  and  back  part  is  a  notch  from  which 
the  mylohyoid  groove  runs  obliquely  downward  and  forward,  and  lodges  the  mylo- 
hyoid vessels  and  nerve.  Behind  this  groove  is  a  rough  surface,  for  the  insertion 
ol  the  Pterygoideus  internus.  The  mandibular  canal  runs  obliquely  downward 
and  forward  in  the  ramus,  and  then  horizontally  forward  in  the  body,  where  it 
is  placed  under  the  alveoli  and  communicates  with  them  by  small  openings.  On 
arriving  at  the  incisor  teeth,  it  turns  back  to  communicate  with  the  mental  foramen, 
giving  off  two  small  canals  which  run  to  the  cavities  containing  the  incisor  teeth. 


■ 


174 


I 


In  the  posterior  two-thirds  of  the  bone  the  canal  is  situated  nearer  the  internal 
surface  of  the  mandible;  and  in  the  anterior  third,  nearer  its  external  surface.  It 
contains  the  inferior  alveolar  vessels  and  nerve,  from  which  branches  are  dis- 
tributed to  the  teeth.  The  lower  border  of  the  ramus  is  thick,  straight,  and  con- 
tinuous W'ith  the  inferior  border  of  the  body  of  the  bone.  At  its  junction  with  the 
posterior  border  is  the  angle  of  the  mandible,  which  may  be  either  inverted  or  everted 
and  is  marked  by  rough,  oblique  ridges  on  each  side,  for  the  attachment  of  the 
Masseter  laterally,  and  the  Pterygoideus  internus  medially;  the  stylomandibular 
ligament  is  attached  to  the  angle  between  these  muscles.  The  anterior  border  is 
thin  above,  thicker  below,  and  continuous  with  the  oblique  line.  The  posterior 
border  is  thick,  smooth,  rounded,  and  covered  by  the  parotid  gland.  The  upper 
border  is  thin,  and  is  surmounted  by  two  processes,  the  coronoid  in  front  and  the 
condyloid  behind,  separated  by  a  deep  concavity,  the  mandibular  notch. 

The  Coronoid  Process  (processus  coronoideus)  is  a  thin,  triangular  eminence, 
which  is  flattened  from  side  to  side  and  varies  in  shape  and  size.  Its  anterior 
border  is  convex  and  is  continuous  below  with  the  anterior  border  of  the  ramus; 
its  posterior  border  is  concave  and  forms  the  anterior  boundary  of  the  mandibular 
notch.  Its  lateral  surface  is  smooth,  and  affords  insertion  to  the  Temporalis  and 
Masseter.  Its  medial  surface  gives  insertion  to  the  Temporalis,  and  presents 
a  ridge  which  begins  near  the  apex  of  the  process  and  runs  downward  and  forward 
to  the  inner  side  of  the  last  molar  tooth.  Between  this  ridge  and  the  anterior 
border  is  a  grooved  triangular  area,  the  upper  part  of  which  gives  attachment 
to  the  Temporalis,  the  lower  part  to  some  fibers  of  the  Buccinator. 

The  Condyloid  Process  (processus  condyloideus)  is  thicker  than  the  coronoid, 
and  consists  of  two  portions :  the  condyle,  and  the  constricted  portion  which  sup- 
ports it,  the  neck.  The  condyle  presents  an  articular  surface  for  articulation  with 
the  articular  disk  of  the  temporomandibular  joint;  it  is  convex  from  before  back- 
ward and  from  side  to  side,  and  extends  farther  on  the  posterior  than  on  the  ante- 
rior surface.  Its  long  axis  is  directed  medialward  and  slightly  backward,  and  if 
prolonged  to  the  middle  line  will  meet  that  of  the  opposite  condyle  near  the  ante- 
rior margin  of  the  foramen  magnum.  At  the  lateral  extremity  of  the  condyle 
is  a  small  tubercle  for  the  attachment  of  the  temporomandibular  ligament.  The 
neck  is  flattened  from  before  backward,  and  strengthened  by  ridges  which  descend 
from  the  forepart  and  sides  of  the  condyle.  Its  posterior  surface  is  convex;  its 
anterior  presents  a  depression  for  the  attachment  of  the  Pterygoideus  externus. 

The  mandibular  notch,  separating  the  two  processes,  is  a  deep  semilunar  depres- 
sion, and  is  crossed  by  the  masseteric  vessels  and  nerve. 

Ossification. — The  mandible  is  ossified  in  the  fibrous  membrane  covering  the  outer  surfaces 
of  Meckel's  cartilages.  These  cartilages  form  the  cartilaginous  bar  of  the  mandibular  arch  (see 
p.  66),  and  are  two  in  number,  a  right  and  a  left.  Their  proximal  or  cranial  ends  are  connected 
with  the  ear  capsules,  and  their  distal  extremities  are  joined  to  one  another  at  the  symphysis 
by  mesodermal  tissue.  They  run  forward  immediately  below  the  condyles  and  then,  bending 
downward,  lie  in  a  groove  near  the  lower  border  of  the  bone;  in  front  of  the  canine  tooth  they 
incUne  upward  to  the  symphysis.  From  the  proximal  end  of  each  cartilage  the  malleus  and 
incus,  two  of  the  bones  of  the  middle  ear,  are  developed;  the  next  succeeding  portion,  as  far  as 
the  lingula,  is  replaced  by  fibrous  tissue,  which  persists  to  form  the  sphenomandibular  ligament. 
Between  the  lingula  and  the  canine  tooth  the  cartilage  disappears,  while  the  portion  of  it  below 
and  behind  the  incisor  teeth  becomes  ossified  and  incorporated  with  this  part  of  the  mandible. 

Ossification  takes  place  in  the  membrane  covering  the  outer  surface  of  the  ventral  end  of 
Meckel's  cartilage  (Figs.  178  to  181),  and  each  half  of  the  bone  is  formed  from  a  single  center 
which  appears,  near  the  mental  foramen,  about  the  sixth  week  of  fetal  life.  By  the  tenth  week 
the  portion  of  Meckel's  cartilage  which  lies  below  and  behind  the  incisor  teeth  is  surrounded  and 
invaded  by  the  membrane  bone.  Somewhat  later,  accessory  nuclei  of  cartilage  make  their  appear- 
ance, viz.,  a  wedge-shaped  nucleus  in  the  condyloid  process  and  extending  downward  through 
the  ramus;  a  small  strip  along  the  anterior  border  of  the  coronoid  process;  and  smaller  nuclei 
in  the  front  part  of  both  alveolar  walls  and  along  the  front  of  the  lower  border  of  the  bone.  These 
accessory  nuclei  possess  no  separate  ossific  centers,  but  are  invaded  by  the  siu-rounding  membrane 


THE  MANDIBLE 


175 


boae  and  undergo  absorption.  The  inner  alveolar  border,  usually  described  as  arising  from  a 
sejjarate  ossific  center  (splenial  center),  is  formed  in  the  human  mandible  by  an  ingrowth  from 
the  main  mass  of  the  bone.  At  birth  the  bone  consists  of  two  parts,  united  by  a  fibrous  symphysis, 
in  which  ossification  takes  place  during  the  first  year. 

The  foregoing  description  of  the  ossification  of  the  mandible  is  based  on  the  researches  of 
Low'  and  Fawcett,-  and  differs  somewhat  from  that  usually  given. 

Articulations. — The  mandible  articulates  with  the  two  temporal  bones. 


Mental  nerve 


Mylohyoid  nerve 

Fio.   178. — Mandible  of  human   embryo  24    mm. 
long.     Outer  aspect.     (From  model  by  Low.) 


Lingual  nerve 
Inf.  alveolar  n. 


Mylohyoid  nerve 
Chorda  tympani 


Stapes 
Facial  nervi 


ReicherVs  cartilage 


Fig.   179. — Mandible  of  human  embryo  24'  mm.  long. 
Inner  aspect.     (From  model  by  Low.) 


Mandibular  nerve 
Meckel's  cartilage 


Mental  nerve 


Anterior  process  of  nuii.i.,^ 

Fig.  180. — Mandible  of  human  embryo  95  mm.  long.     Outer  aspect.     Nuclei  of  cartilage  stippled. 

(From  model  by  Low.) 


AuriciUotem/poral  nerve 


Ant.  process  of  malleus 
Chorda  tympani 


Symphysis 


stylohyoid  nerve 


Fig.  181.- 


-Mandible  of  human  embryo  95  mm.  long.     Inner  aspect. 
(From  model  by  Low.) 


Nuclei  of  cartilage  stippled. 


CHANGES  PRODUCED  IN  THE  MANDIBLE  BY  AGE. 


At  birth  (Fig.  182)  the  body  of  the  bone  is  a  mere  shell,  containing  the  sockets  of  the  two 
incisor,  the  canine,  and  the  two  deciduous  molar  teeth,  imperfectly  partitioned  off  from  one 
another.  The  mandibular  canal  is  of  large  size,  and  runs  near  the  lower  border  of  the  bone;  the 
m<mtal  foramen  opens  beneath  the  socket  of  the  first  deciduous  molar  tooth.  The  angle  is  obtuse 
(175°),  and  the  condyloid  portion  is  nearly  in  Une  with  the  body.  The  coronoid  process  is  of 
comparatively  large  size,  and  projects  above  the  level  of  the  condyle. 

•  Proceedings  of  the  Anatomical  and  -Anthropological  Society  of  the  University  of  Aberdeen,  1905,  and  Journal  of 
Anatomy  and  Physiology,  vol.  xliv. 

•  Journal  of  the  American  Medical  Association,  September  2,  1905. 


OSTEOLOGY 


Fi3.  182.— At  birth. 


Fig.  183. — In  chUdhood. 


Fig.  184.— In  the  adult. 


Fig.  185.— In  old  age. 
Side  view  of  the  mandible  at  different  periods  of  life. 


THE  HYOID  BONE 


177 


After  birth  (Fig.  183)  the  two  segments  of  the  bone  become  joined  at  the  symphysis,  from 
below  upward,  in  the  first  year;  but  a  trace  of  separation  may  be  visible  in  the  beginning  of  the 
second  year,  near  the  alveolar  margin.  The  body  becomes  elongated  in  its  whole  length,  but 
more  especially  behind  the  mental  foramen,  to  provide  space  for  the  three  additional  teeth  devel- 
oped in  this  part.  The  depth  of  the  body  increases  owing  to  increased  growth  of  the  alveolar 
part,  to  afford  room  for  the  roots  of  the  teeth,  and  by  thickening  of  the  subdental  portion  which 
enables  the  jaw  to  withstand  the  powerful  action  of  the  masticatory  muscles;  but  the  alveolar 
portion  is  the  deeper  of  the  two,  and,  consequently,  the  chief  part  of  the  body  hes  above  the 
oblique  line.  The  mandibular  canal,  after  the  second  dentition,  is  situated  just  above  the  level 
of  the  mylohyoid  line;  and  the  mental  foramen  occupies  the  position  usual  to  it  in  the  adult. 
The  angle  becomes  less  obtuse,  owing  to  the  separation  of  the  jaws  by  the  teeth;  about  the  fourth 
year  it  is  140°. 

In  the  adult  (Fig.  184)  the  alveolar  and  subdental  portions  of  the  body  are  usually  of  equal 
depth.  The  mental  foramen  opens  midway  between  the  upper  and  lower  borders  of  the  bone, 
and  the  mandibular  canal  runs  nearly  parallel  with  the  mylohyoid  line.  The  ramus  is  almost 
vertical  in  direction,  the  angle  measuring  from  110°  to  120°. 

In  old  age  (Fig.  185)  the  bone  becomes  greatly  reduced  in  size,  for  with  the  loss  of  the  teeth 
the  alveolar  process  is  absorbed,  and,  consequently,  the  chief  part  of  the  bone  is  below  the  oblique 
line.  The  mandibular  canal,  with  the  mental  foramen  opening  from  it,  is  close  to  the  alveolar 
border.  The  ramus  is  obUque  in  direction,  the  angle  measures  about  140°,  and  the  neck  of  the 
condyle  is  more  or  less  bent  backward. 


The  Hyoid  Bone  (Os  Hyoideum;  Lingual  Bone). 


The  hyoid  bone  is  shaped  hke  a  horseshoe,  and  is  suspended  from  the  tips  of  the 
styloid  processes  of  the  temporal  bones  by  the  stylohyoid  ligaments.  It  consists 
of  five  segments,  viz.,  a  body,  two  greater  comua,  and  two  lesser  comua. 

The  Body  or  Basihyal  (corpus  oss.  hyoidei). — ^The  body  or  central  part  is 
of  a  quadrilateral  form.  Its  anterior  surface  (Fig.  186)  is  convex  and  directed 
forward  and  upward.  It  is  crossed  in  its  upper  half  by  a  well-marked  transverse 
ridge  with  a  slight  downward 
convexity,  and  in  many  cases  i<^;  ^Greater  comu 

a  vertical  median  ridge  divides 
it  into  two  lateral  halves. 
The  portion  of  the  vertical 
ridge  above  the  transverse  line 
is  present  in  a  majority  of 
^pecimens,  but  the  lower  por- 
lion  is  evident  only  in  rare 
cases.  The  anterior  surface 
j;ives  insertion  to  the  Genio- 
liyoideus  in  the  greater  part 
of  its  extent  both  above  and 
below  the  transverse  ridge;  a 
])ortion  of  the  origin  of  the 
llyoglossus  notches  the  lateral 

inargin  of  the  Geniohyoideus  attachment.  Below  the  transverse  ridge  the  Mylo- 
hyoideus,  Sternohyoideus,  and  Omohyoideus  are  inserted.  The  posterior  surface  is 
^mooth,  concave,  directed  backward  and  downward,  and -separated  from  the  epi- 
[,'lottis  by  the  hyothyroid  membrane  and  a  quantity  of  loose  areolar  tissue;  a  bursa 
intervenes  between  it  and  the  hyothyroid  membrane.  The  superior  border  is 
rounded,  and  gives  attachment  to  the  hyothyroid  membrane  and  some  aponeurotic 
libers  of  the  Genioglossus.  The  inferior  border  affords  insertion  medially  to  the 
Sternohyoideus  and  laterally  to  the  Omohyoideus  and  occasionally  a  portion  of  the 
Thyreohyoideus.  It  also  gives  attachment  to  the  Levator  glandulae  thyreoidese, 
^vhen  this  muscle  is  present.  In  early  life  the  lateral  borders  are  connected  to 
the  greater  cornua  by  synchondroses;  after  middle  life  usually  by  bony  union. 
12  ' 


DIGASTRICUS  & 
STYLOHYOIDEUS 

\      THYREOHYOIDECS 

Omohyoideus 


/     mtlohtordeus     sternohyoideus 
Geniohyoideus 

Fig.   186. — Hyoid  bone.     Anterior  surface.     Enlarged. 


178  '^^^^^^^-         OSTEOLOGY 


I 


The  Greater  Cornua  or  Thyrohyals  (cornua  majora) .  — The  greater  cornua 
project  backward  from  the  lateral  borders  of  the  body;  they  are  flattened  from 
above  downward  and  diminish  in  size  from  before  backward;  each  ends  in  a  tubercle 
to  which  is  fixed  the  lateral  hyothyroid  ligament.  The  upper  surface  is  rough 
close  to  its  lateral  border,  for  muscular  attachments:  the  largest  of  these  are  the 
origins  of  the  Hyoglossus  and  Constrictor  pharyngis  medius  which  extend  along 
the  whole  length  of  the  cornu;  the  Digastricus  and  Stylohyoideus  have  small 
insertions  in  front  of  these  near  the  junction  of  the  body  with  the  cornu.  To  the 
medial  border  the  hyothyroid  membrane  is  attached,  while  the  anterior  half  of  the 
lateral  border  gives  insertion  to  the  Thyreohyoideus. 

The  Lesser  Cornua  or  Ceratohyals  {cornua  minora). — The  lesser  cornu  are  two 
small,  conical  eminences,  attached  by  their  bases  to  the  angles  of  junction  between 
the  body  and  greater  cornua.  They  are  connected  to  the  body  of  the  bone  by  fibrous 
tissue,  and  occasionally  to  the  greater  cornua  by  distinct  diarthrodial  joints, 
which  usually  persist  throughout  life,  but  occasionally  become  ankylosed. 

The  lesser  cornua  are  situated  in  the  line  of  the  transverse  ridge  on  the  body 
and  appear  to  be  morphological  continuations  of  it  (Parsons^) .  The  apex  of  each 
cornu  gives  attachment  to  the  stylohyoid  ligament ;2  the  Chondroglossus  rises 
from  the  medial  side  of  the  base. 

Ossification. — The  hyoid  is  ossified  from  six  centers:  two  for  the  body,  and  one  for  each  cornu. 
Ossification  commences  in  the  greater  cornua  toward  the  end  of  fetal  life,  in  the  body  shortly 
afterward,  and  in  the  lesser  cornua  during  the  first  or  second  year  after  birth. 


THE    EXTERIOR    OF    THE    SKULL. 

The  skull  as  a  whole  may  be  viewed  from  different  points,  and  the  views  so 
obtained  are  termed  the  nomise  of  the  skull ;  thus,  it  may  be  examined  from  above 
(norma  verticalis),  from  below  (norma  basalis),  from  the  side  (norma  lateralis), 
from  behind  (norma  occipitalis),  or  from  the  front  (norma  frontalis). 

Norma  Verticalis.— When  viewed  from  above  the  outline  presented  varies 
greatly  in  different  skulls;  in  some  it  is  more  or  less  oval,  in  others  more  nearly 
circular.  The  surface  is  traversed  by  three  sutures,  viz.:  (1)  the  coronal  sutures, 
nearly  transverse  in  direction,  between  the  frontal  and  parietals;  (2)  the  sagittal 
sutures,  medially  placed,  between  the  parietal  bones,  and  deeply  serrated  in  its 
anterior  two-thirds;  and  (3)  the  upper  part  of  the  lambdoidal  suture,  between  the 
parietals  and  the  occipital.  The  point  of  junction  of  the  sagittal  and  coronal  suture 
is  named  the  bregma,  that  of  the  sagittal  and  lambdoid  sutures,  the  lambda;  they 
indicate  respectively  the  positions  of  the  anterior  and  posterior  fontanelles  in  the 
fetal  skull.  On  either  side  of  the  sagittal  suture  are  the  parietal  eminence  and  parietal 
foramen — the  latter,  however,  is  frequently  absent  on  one  or  both  sides.  The 
skull  is  often  somewhat  flattened  in  the  neighborhood  of  the  parietal  foramina, 
and  the  term  obelion  is  applied  to  that  point  of  the  sagittal  suture  which  is  on 
a  level  with  the  foramina.  In  front  is  the  glabella,  and  on  its  lateral  aspects  are 
the  superciliary  arches,  and  above  these  the  frontal  eminences.  Immediately  above 
the  glabella  may  be  seen  the  remains  of  the  frontal  suture;  in  a  small  percentage 
of  skulls  this  suture  persists  and  extends  along  the  middle  line  to  the  bregma. 
Passing  backward  and  upward  from  the  zygomatic  processes  of  the  frontal  bone 
are  the  temporal  lines,  which  mark  the  upper  limits  of  the  temporal  fossae.  The 
zygomatic  arches  may  or  may  not  be  seen  projecting  beyond  the  anterior  portions 
of  these  lines. 

1  See  article  on  "The  Topography  and  Morphology  of  the  Human  Hyoid  Bone,"  by  F.  G.  Parsons,  Journal  of 
Anatomy  and  Physiology,  vol.  xliii. 

2  These  ligaments  in  many  animals  are  distinct  bones,  and  in  man  may  undergo  partial  ossification. 


THE  EXTERIOR  OF  THE  SKULL 


179 


Norma  Basalis  (Fig.  187).- — The  inferior  surface  of  the  base  of  the  skull,  exclu- 
sive of  the  mandible,  is  bounded  in  front  by  the  incisor  teeth  in  the  maxillae;  behind, 


Incisors 


Incisive  canal 


Transmits  left  nasopalatine  nerve 
Transmits  descending  palatine  vesseU 
Transmits  right  nasopalatine  nerve 


Lesser  palatine  foramina 

Posterior  nasal  spine 
Musculus  uvulae 
Pterygoid  hamulus 


Sphenoidal  process  of  palatine 

Pharyngeal  canal 


Tensor  tympani 

Pharyngeal  tubercle 
Situation  of  auditory  tube  and 
liasiiar    '^      Semicanal  foT  TcnsoT  tympani 

\:  '  -part— Tensor  veli  palatini 

S^?i.j^^'^°" inferior  tympanic  canaliculus 

Aquaednctus  cochleae 

Jugular  foramen 
Mastoid  canaliculus 
Tympanomastoid  fissure 


Fig.  187.— I 


one^ 

of  skull.     Inferior  surface. 


180 


OSTEOLOGY 


I 


by  the  superior  nuchal  lines  of  the  occipital;  and  laterally  by  the  alveolar  arch, 
the  lower  border  of  the  zygomatic  bone,  the  zygomatic  arch  and  an  imaginary 
line  extending  from  it  to  the  mastoid  process  and  extremity  of  the  superior  nuchal 
line  of  the  occipital.  It  is  formed  by  the  palatine  processes  of  the  maxillae  and 
palatine  bones,  the  vomer,  the  pterygoid  processes,  the  under  surfaces  of  the 
great  wings,  spinous  processes,  and  part  of  the  body  of  the  sphenoid,  the  under 
surfaces  of  the  squamae  and  mastoid  and  petrous  portions  of  the  temporals,  and 
the  under  surface  of  the  occipital  bone.  The  anterior  part  or  hard  palate  projects 
below  the  level  of  the  rest  of  the  surface,  and  is  bounded  in  front  and  laterally 
by  the  alveolar  arch  containing  the  sixteen  teeth  of  the  maxillae.  Immediately 
behind  the  incisor  teeth  is  the  incisive  foramen.  In  this  foramen  are  two  lateral 
apertures,  the  openings  of  the  incisive  canals  (foramina  of  Stenson)  which  transmit 
the  anterior  branches  of  the  descending  palatine  vessels,  and  the  nasopalatine 
nerves.  Occasionally  two  additional  canals  are  present  in  the  incisive  foramen; 
they  are  termed  the  foramina  of  Scarpa  and  are  situated  in  the  middle  line;  when 
present  they  transmit  the  nasopalatine  nerves.  The  vault  of  the  hard  palate 
is  concave,  uneven,  perforated  by  numerous  foramina,  marked  by  depressions  for 
the  palatine  glands,  and  traversed  by  a  crucial  suture  formed  by  the  junction  of  the 
four  bones  of  which  it  is  composed.  In  the  young  skull  a  suture  may  be  seen  ex- 
tending on  either  side  from  the  incisive  foramen  to  the  interval  between  the  lateral 
incisor  and  canine  teeth,  and  marking  off  the  os  incisivum  or  premaxillary  bone. 
At  either  posterior  angle  of  the  hard  palate  is  the  greater  palatine  foramen,  for  the 
transmission  of  the  descending  palatine  vessels  and  anterior  palatine  nerve;  and 
running  forward  and  medialward  from  it  a  groove,  for  the  same  vessels  and  nerve. 
Behind  the  posterior  palatine  foramen  is  the  pyramidal  process  of  the  palatine  bone, 
perforated  by  one  or  more  lesser  palatine  foramina,  and  marked  by  the  commence- 
ment of  a  transverse  ridge,  for  the  attachment  of  the  tendinous  expansion  of  the 
Tensor  veli  palatini.  Projecting  backward  from  the  center  of  the  posterior  border 
of  the  hard  palate  is  the  posterior  nasal  spine,  for  the  attachment  of  the  Musculus 
uvulae.  Behind  and  above  the  hard  palate  are  the  choanse,  measuring  about 
2.5  cm.  in  their  vertical  and  1.25  cm.  in  their  transverse  diameters.  They  are 
separated  from  one  another  by  the  vomer,  and  each  is  bounded  above  by  the  body 
of  the  sphenoid,  below  by  the  horizontal  part  of  the  palatine  bone,  and  laterally 
by  the  medial  pterygoid  plate  of  the  sphenoid.  At  the  superior  border  of  the 
vomer  may  be  seen  the  expanded  alae  of  this  bone,  receiving  between  them  the  ros- 
trum of  the  sphenoid.  Near  the  lateral  margins  of  the  alae  of  the  vomer,  at  the 
roots  of  the  pterygoid  processes,  are  the  pharyngeal  canals.  The  pterygoid  process 
presents  near  its  base  the  pterygoid  canal,  for  the  transmission  of  a  nerve  and  artery. 
The  medial  pterygoid  plate  is  long  and  narrow;  on  the  lateral  side  of  its  base  is  the 
scaphoid  fossa,  for  the  origin  of  the  Tensor  veli  palatini,  and  at  its  lower  extremity 
the  hamulus,  around  which  the  tendon  of  this  muscle  turns.  The  lateral  pterygoid 
plate  is  broad;  its  lateral  surface  forms  the  medial  boundary  of  the  infratemporal 
fossa,  and  affords  attachment  to  the  Pterygoideus  externus. 

Behind  the  nasal  cavities  is  the  basilar  portion  of  the  occipital  bone,  presenting 
near  its  center  the  pharyngeal  tubercle  for  the  attachment  of  the  fibrous  raphe 
of  the  pharynx,  Avith  depressions  on  either  side  for  the  insertions  of  the  Rectus 
capitis  anterior  and  Longus  capitis.  At  the  base  of  the  lateral  pterygoid  plate 
is  the  foramen  ovale,  for  the  transmission  of  the  mandibular  nerve,  the  accessory 
meningeal  artery,  and  sometimes  the  lesser  superficial  petrosal  nerve;  behind  this  are 
the  foramen  spinosum  which  transmits  the  middle  meningeal  vessels,  and  the  promi- 
nent spina  angularis  {sphenoidal  spine),  which  gives  attachment  to  the  spheno- 
mandibular  ligament  and  the  Tensor  veli  palatini.  Lateral  to  the  spina  angularis 
is  the  mandibular  fossa,  divided  into  two  parts  by  the  petrotympanic  fissure;  the 
anterior  portion,  concave,    smooth,  bounded  in  front  by  the  articular  tubercle, 


THE  EXTERIOR  OF  THE  SKULL  181 


I 


serves  for  the  articulation  of  the  condyle  of  the  mandible;  the  posterior  portion, 
rough  and  bounded  behind  by  the  tympanic  part  of  the  temporal,  is  sometimes 
occupied  by  a  part  of  the  parotid  gland.  Emerging  from  between  the  laminae 
of  the  vaginal  process  of  the  tympanic  part  is  the  styloid  process;  and  at  the  base 
of  this  process  is  the  stylomastoid  foramen,  for  the  exit  of  the  facial  nerve,  and 
entrance  of  the  stylomastoid  artery.  Lateral  to  the  stylomastoid  foramen,  between 
the  tympanic  part  and  the  mastoid  process,  is  the  tympanomastoid  fissure,  for  the 
auricular  branch  of  the  vagus.  Upon  the  medial  side  of  the  mastoid  process  is 
the  mastoid  notch  for  the  posterior  belly  of  the  Digastricus,  and  medial  to  the  notch, 
the  occipital  groove  for  the  occipital  artery.  At  the  base  of  the  medial  pterygoid 
plate  is  a  large  and  somewhat  triangular  aperture,  the  foramen  lacerum,  bounded 
in  front  by  the  great  wing  of  the  sphenoid,  behind  by  the  apex  of  the  petrous 
portion  of  the  temporal  bone,  and  medially  by  the  body  of  the  sphenoid  and  basilar 
portion  of  the  occipital  bone;  it  presents  in  front  the  posterior  orifice  of  the  ptery- 
goid canal;  behind,  the  aperture  of  the  carotid  canal.  The  lower  part  of  this  opening 
IS  filled  up  in  the  fresh  state  by  a  fibrocartilaginous  plate,  across  the  upper  or 
cerebral  surface  of  which* the  internal  carotid  artery  passes.  Lateral  to  this  aperture 
is  a  groove,  the  sulcus  tubse  auditivse,  between  the  petrous  part  of  the  temporal  and 
the  great  wing  of  the  sphenoid.  This  sulcus  is  directed  lateralward  and  backward 
from  the  root  of  the  medial  pterygoid  plate  and  lodges  the  cartilaginous  part  of  the 
auditory  tube;  it  is  continuous  behind  with  the  canal  in  the  temporal  bone  which 
forms  the  bony  part  of  the  same  tube.  At  the  bottom  of  this  sulcus  is  a  narrow 
cleft,  the  petrosphenoidal  fissure,  which  is  occupied,  in  the  fresh  condition,  by  a 
P'late  of  cartilage.  Behind  this  fissure  is  the  under  surface  of  the  petrous  portion 
cf  the  temporal  bone,  presenting,  near  its  apex,  the  quadrilateral  rough  surface, 
part  of  which  affords  attachment  to  the  Levator  veli  palatini ;  lateral  to  this  surface 
is  the  orifice  of  the  carotid  canal,  and  medial  to  it,  the  depression  leading  to  the 
aquseductus  cochleae,  the  former  transmitting  the  internal  carotid  artery  and  the 
( arotid  plexus  of  the  sympathetic,  the  latter  serving  for  the  passage  of  a  vein  from 
the  cochlea.  Behind  the  carotid  canal  is  the  jugular  foramen,  a  large  aperture, 
formed  in  front  by  the  petrous  portion  of  the  temporal,  and  behind  by  the  occipital ; 
it  is  generally  larger  on  the  right  than  on  the  left  side,  and  may  be  subdivided 
into  three  compartments.  The  anterior  compartment  transmits  the  inferior 
])etrosal  sinus;  the  intermediate,  the  glossopharyngeal,  vagus,  and  accessory 
nerves;  the  posterior,  the  transverse  sinus  and  some  meningeal  branches  from  the 
occipital  and  ascending  pharyngeal  arteries.  On  the  ridge  of  bone  dividing  the 
carotid  canal  from  the  jugular  foramen  is  the  inferior  tympanic  canaliculus  for 
the  transmission  of  the  tympanic  branch  of  the  glossopharyngeal  nerve;  and  on  the 
wall  of  the  jugular  foramen,  near  the  root  of  the  styloid  process,  is  the  mastoid 
canaliculus  for  the  passage  of  the  auricular  branch  of  the  vagus  nerve.  Extending 
J'orward  from  the  jugular  foramen  to  the  foramen  lacerum  is  the  petrooccipital  fissure 
occupied,  in  the  fresh  state,  by  a  plate  of  cartilage.  Behind  the  basilar  portion 
ot  the  occipital  bone  is  the  foramen  magnum,  bounded  laterally  by  the  occipital 
condyles,  the  medial  sides  of  which  are  rough  for  the  attachment  of  the  alar 
ligaments.  Lateral  to  each  condyle  is  the  jugular  process  which  gives  attachment 
■zo  the  Rectus  capitis  lateralis  muscle  and  the  lateral  atlantooccipital  ligament. 
The  foramen  magnum  transmits  the  medulla  oblongata  and  its  membranes,  the 
accessory  nerves,  the  vertebral  arteries,  the  anterior  and  posterior  spinal  arteries, 
and  the  ligaments  connecting  the  occipital  bone  with  the  axis.  The  mid-points 
on  the  anterior  and  posterior  margins  of  the  foramen  magnum  are  respectively 
termed  the  basion  and  the  opisthion.  In  front  of  each  condyle  is  the  canal  for  the 
passage  of  the  hypoglossal  nerve  and  a  meningeal  artery.  Behind  each  condyle 
is  the  condyloid  fossa,  perforated  on  one  or  both  sides  by  the  condyloid  canal,  for 
the  transmission  of  a  vein  from  the  transverse  sinus.    Behind  the  foramen  magnum 


182 


OSTEOLOGY 


is  the  median  nuchal  line  ending  above  at  the  external  occipital  protuberance,  while 
on  either  side  are  the  superior  and  inferior  nuchal  lines;  these,  as  well  as  the  surfaces 
of  bone  between  them,  are  rough  for  the  attachment  of  the  muscles  which  are 
enumerated  on  pages  129  and  130. 

Norma  Lateralis  (Fig.  188). — When  viewed  from  the  side  the  skull  is  seen  to 
consist  of  the  cranium  above  and  behind,  and  of  the  face  below  and  in  front.  The 
cranium  is  somewhat  ovoid  in  shape,  but  its  contour  varies  in  different  cases  and 
depends  largely  on  the  length  and  height  of  the  skull  and  on  the  degree  of  promi- 
nence of  the  superciliary  arches  and  frontal  eminences.  Entering  into  its  formation 
are  the  frontal,  the  parietal,  the  occipital,  the  temporal,  and  the  great  wing  of  the 


Fig.  188. — Side  view  of  the  skull. 

sphenoid.  These  bones  are  joined  to  one  another  and  to  the  zygomatic  by  the  follow- 
ing sutures :  the  zygomaticotemporal  between  the  zygomatic  process  of  the  temporal 
and  the  temporal  process  of  the  zygomatic;  the  zygomaticofrontal  uniting  the  zygo- 
matic bone  with  the  zygomatic  process  of  the  frontal ;  the  sutures  surrounding  the 
great  wing  of  the  sphenoid,  viz.,  the  sphenozygomatic  in  front,  the  sphenofrontal 
and  sphenoparietal  above,  and  the  sphenosquamosal  behind.  The  sphenoparietal 
suture  varies  in  length  in  different  skulls,  and  is  absent  in  those  cases  where  the 
frontal  articulates  with  the  temporal  squama.  The  point  corresponding  with  the 
posterior  end  of  the  sphenoparietal  suture  is  named  the  pterion;  it  is  situated  about 
3  cm.  behind,  and  a  little  above  the  level  of  the  zygomatic  process  of  the  frontal 
bone. 


THE  EXTERIOR  OF  THE  SKULL  183 

The  squamosal  suture  arches  backward  from  the  pterion  and  connects  the  tem- 
poral squama  with  the  lower  border  of  the  parietal:  this  suture  is  continuous 
behind  with  the  short,  nearly  horizontal  parietomastoid  suture,  which  unites  the 
mastoid  process  of  the  temporal  with  the  region  of  the  mastoid  angle  of  the  parietal. 
Extending  from  above  downward  and  forward  across  the  cranium  are  the  coronal 
and  lambdoidal  sutures;  the  former  connects  the  parietals  with  the  frontal,  the  latter, 
the  parietals  with  the  occipital.  The  lambdoidal  suture  is  continuous  below  with 
the  occipitomastoid  suture  between  the  occipital  and  the  mastoid  portion  of  the 
temporal.  In  or  near  the  last  suture  is  the  mastoid  foramen,  for  the  transmission 
of  an  emissary  vein.  The  point  of  meeting  of  the  parietomastoid,  occipitomastoid, 
and  lambdoidal  sutures  is  known  as  the  asterion.  Immediately  above  the  orbital 
margin  is  the  superciliary  arch,  and,  at  a  higher  level,  the  frontal  eminence.  Near 
the  center  of  the  parietal  bone  is  the  parietal  eminence.  Posteriorly  is  the  ex- 
ternal occipital  protuberance,  from  which  the  superior  nuchal  line  may  be  followed 
forward  to  the  mastoid  process.  Arching  across  the  side  of  the  cranium  are  the 
temporal  lines,  which  mark  the  upper  limit  of  the  temporal  fossa. 

The  Temporal  Fossa  (fossa  temporalis). — The  temporal  fossa  is  bounded  above 
and  behind  by  the  temporal  lines,  which  extend  from  the  zygomatic  process  of  the 
frontal  bone  upward  and  backward  across  the  frontal  and  parietal  bones,  and  then 
curve  downward  and  forward  to  become  continuous  with  the  supramastoid  crest 
and  the  posterior  root  of  the  zygomatic  arch.  The  point  where  the  upper  temporal 
line  cuts  the  coronal  suture  is  named  the  stephanion.  The  temporal  fossa  is  bounded 
in  front  by  the  frontal  and  zygomatic  bones,  and  opening  on  the  back  of  the  latter 
is  the  zygomaticotemporal  foramen.  Laterally  the  fossa  is  limited  by  the  zygomatic 
arch,  formed  by  the  zygomatic  and  temporal  bones;  below,  it  is  separated  from  the 
infratemporal  fossa  by  the  infratemporal  crest  on  the  great  wing  of  the  sphenoid, 
and  by  a  ridge,  continuous  with  this  crest,  which  is  carried  backward  across  the 
temporal  squama  to  the  anterior  root  of  the  zygomatic  process.  In  front  and 
1  elow,  the  fossa  communicates  with  the  orbital  cavity  through  the  inferior  orbital 
(  r  sphenomaxillary  fissure.  The  floor  of  the  fossa  is  deeply  concave  in  front  and 
( onvex  behind,  and  is  formed  by  the  zygomatic,  frontal,  parietal,  sphenoid,  and 
temporal  bones.  It  is  traversed  by  vascular  furrows;  one,  usually  well-marked,  runs 
upward  above  and  in  front  of  the  external  acoustic  meatus,  and  lodges  the  middle 
temporal  artery.  Two  others,  frequently  indistinct,  may  be  observed  on  the 
J  nterior  part  of  the  floor,  and  are  for  the  anterior  and  posterior  deep  temporal 
jTteries.  The  temporal  fossa  contains  the  Temporalis  muscle  and  its  vessels  and 
nerves,  together  with  the  zygomaticotemporal  nerve. 

The  zygomatic  arch  is  formed  by  the  zygomatic  process  of  the  temporal  and 

1  he  temporal  process  of  the  zygomatic,  the  two  being  united  by  an  oblique  suture ; 

i.he  tendon  of  the  Temporalis  passes  medial  to  the  arch  to  gain  insertion  into  the 

'oronoid  process  of  the  mandible.    The  zygomatic  process  of  the  temporal  arises 

l)y  two  roots,  an  anterior,  directed  inward  in  front  of  the  mandibular  fossa,  where 

^■it  expands  to  form  the  articular  tubercle,  and  a  posterior,  which  runs  backward 

^■above  the  external  acoustic  meatus  and  is  continuous  with  the  supramastoid 

<:rest.     The  upper  border  of  the  arch  gives  attachment  to  the  temppral  fascia; 

■the  lower  border  and  medial  surface  give  origin  to  the  Masseter. 
Below  the  posterior  root  of  the  zygomatic  arch  is  the  elliptical  orifice  of  the 
external  acoustic  meatus,  bounded  in  front,  below,  and  behind  by  the  tympanic 
part  of  the  temporal  bone;  to  its  outer  margin  the  cartilaginous  segment  of  the 
external  acoustic  meatus  is  attached.  The  small  triangular  area  between  the 
posterior  root  of  the  zygomatic  arch  and  the  postero-superior  part  of  the  orifice  is 
termed  the  suprameatal  triangle,  on  the  anterior  border  of  which  a  small  spinous 
process,  the  suprameatal  spine,  is  sometimes  seen.     Between  the  tympanic  part 

I  and  the  articular  tubercle  is  the  mandibular  fossa,  divided  into  two  parts  bv  the 
1 


] 

I 


184 


OSTEOLOGY 


petrotympanic  fissure.  The  anterior  and  larger  part  of  the  fossa  articulates  A^'ith 
the  condyle  of  the  mandible  and  is  limited  behind  by  the  external  acoustic  meatus  r 
the  posterior  part  sometimes  lodges  a  portion  of  the  parotid  gland.  The  styloid 
process  extends  downward  and  forward  for  a  variable  distance  from  the  lower 
part  of  the  tympanic  part,  and  gives  attachment  to  the  Styloglossus,  Stylo hy- 
oideus,  and  Stylopharyngeus,  and  to  the  stylohyoid  and  stylomandibular  ligaments. 
Projecting  downward  behind  the  external  acoustic  meatus  is  the  mastoid  process, 
to  the  outer  surface  of  which  the  Sternocleidomastoideus,  Splenius  capitis,  and 
Longissimus  capitis  are  attached. 

The  Infratemporal  Fossa  (fossa  infratemporalis;  zygomatic  fossa)  (Fig.  189). — 1'he 
infratemporal  fossa  is  an  irregularly  shaped  cavity,  situated  below  and  medial  to  the 
zygomatic  arch.    It  is  bounded,  in  front,  by  the  infratemporal  surface  of  the  maxilla 


m  Parietc 


/     Fronlof 


Sf/uama 

of  lempoTal 


Inferior  orbital  fissure 

Infratemporal  crest 

Pterygomaxillary  fissm  e 


External  acoustic  meatus 
Tympanic  part  of  temporal 
Styloid  process 
Mandibular  cavity 
Zygomatic  process  {cut) 
Lateral  pterygoid  plate 


Pterygoid  hamulus 

Fig.   189. — Left  infratemporal  fossa. 


and  the  ridge  which  descends  from  its  zygomatic  process;  behind,  by  the  articular 
tubercle  of  the  temporal  and  the  spina  angularis  of  the  sphenoid;  above,  by  the  great 
wing  of  the  sphenoid  below  the  infratemporal  crest,  and  by  the  under  surface  of 
the  temporal  squama;  below,  by  the  alveolar  border  of  the  maxilla;  medially,  by 
the  lateral  pterygoid  plate.  It  contains  the  lower  part  of  the  Temporalis,  the 
Pterygoidei  internus  and  externus,  the  internal  maxillary  vessels,  and  the  man- 
dibular and  maxillary  nerves.  The  foramen  ovale  and  foramen  spinosum  open  on 
its  roof,  and  the  alveolar  canals  on  its  anterior  wall.  At  its  upper  and  medial 
part  are  two  fissures,  which  together  form  a  T-shaped  fissure,  the  horizontal  limb 
being  named  the  inferior  orbital,  and  the  vertical  one  the  pterygomaxillary. 

The  inferior  orbital  fissure  (fissura  orbitalis  inferior;  sphenomaxillary  fissnre), 
horizontal  in  direction,  opens  into  the  lateral  and  back  part  of  the  orbit.  It  is 
bounded  above  by  the  lower  border  of  the  orbital  surface  of  the  great  wing  of  the 


THE  EXTERIOR  OF  THE  SKULL  185 

sphenoid;  below,  by  the  lateral  border  of  the  orbital  sirt-face  of  the  maxilla  and  the 
orbital  process  of  the  palatine  bone;  laterally,  by  a  small  part  of  the  zygomatic 
bone  :^  medially,  it  joins  at  right  angles  with  the  pterygomaxillary  fissure.  Through 
the  inferior  orbital  fissure  the  orbit  communicates  with  the  temporal,  infratem- 
poral, and  pterygopalatine  fossae;  the  fissure  transmits  the  maxillary  nerve  and 
its  zygomatic  branch,  the  infraorbital  vessels,  the  ascending  branches  from  the 
sphenopalatine  ganglion,  and  a  vein  which  connects  the  inferior  ophthalmic  vein 
with  the  pterygoid  venous  plexus. 

The  pterygomaxillary  fissure  is  vertical,  and  descends  at  right  angles  from  the 
medial  end  of  the  preceding;  it  is  a  triangular  interval,  formed  by  the  diver- 
gence of  the  maxilla  from  the  pterygoid  process  of  the  sphenoid.  It  connects 
the  infratemporal  with  the  pterygopalatine  fossa,  and  transmits  the  terminal  part 
of  the  internal  maxillary  artery. 

The  Pterygopalatine  Fossa  (fossa  pterygopalatina;  sphenomaxillary  fossa) . — ^The 
pterygopalatine  fossa  is  a  small,  triangular  space  at  the  angle  of  junction  of  the 
inferior  orbital  and  pterygomaxillary  fissures,  and  placed  beneath  the  apex  of 
the  orbit.  It  is  bounded  above  by  the  under  surface  of  the  body  of  the  sphenoid 
and  by  the  orbital  process  of  the  palatine  bone;  in  front,  by  the  infratemporal 
surface  of  the  maxilla;  behind,  by  the  base  of  the  pterygoid  process  and  lower  part 
of  the  anterior  surface  of  the  great  wing  of  the  sphenoid ;  medially,  by  the  vertical 
part  of  the  palatine  bone  with  its  orbital  and  sphenoidal  processes.  This  fossa 
communicates  with  the  orbit  by  the  inferior  orbital  fissure,  with  the  nasal  cavity 
by  the  sphenopalatine  foramen,  and  with  the  infratemporal  fossa  by  the  pterygo- 
maxillary fissure.  Five  foramina  open  into  it.  Of  these,  three  are  on  the  posterior 
V  all,  viz.,  the  foramen  rotimdum,  the  pterygoid  canal,  and  the  pharyngeal  canal, 
in  this  order  downward  and  medialward.  On  the  medial  wall  is  the  sphenopalatine 
foramen,  and  below  is  the  superior  orifice  of  the  pterygopalatine  canal.  The  fossa 
contains  the  maxillary  nerve,  the  sphenopalatine  ganglion,  and  the  terminal  part 
of  the  internal  maxillary  artery. 

Norma  Occipitalis. — When  viewed  from  behind  the  cranium  presents  a  more 
or  less  circular  outline.  In  the  middle  line  is  the  posterior  part  of  the  sagittal 
sature  connecting  the  parietal  bones;  extending  downward  and  lateralward  from 
the  hinder  end  of  the  sagittal  suture  is  the  deeply  serrated  lambdoidal  suture  join- 
i  ig  the  parietals  to  the  occipital  and  continuous  below  with  the  parietomastoid  and 
occipitomastoid  sutures;  it  frequently  contains  one  or  more  sutural  bones.  Near 
the  middle  of  the  occipital  squama  is  the  external  occipital  protuberance  or  inion, 
and  extending  lateralward  from  it  on  either  side  is  the  superior  nuchal  line,  and 
above  this  the  faintly  marked  highest  nuchal  line.  The  part  of  the  squama  above 
the  inion  and  highest  lines  is  named  the  planum  occipitale,  and  is  covered  by  the 
Occipitalis  muscle;  the  part  below  is  termed  the  planum  nuchale,  and  is  divided 
by  the  median  nuchal  line  which  runs  downward  and  forward  from  the  inion  to  the 
faramen  magnum;  this  ridge  gives  attachment  to  the  ligamentum  nuchae.  The 
muscles  attached  to  the  planum  nuchale  are  enumerated  on  p.  130.  Below  and  in 
front  are  the  mastoid  processes,  convex  laterally  and  grooved  medially  b}^  the 
mastoid  notches.  In  or  near  the  occipitomastoid  suture  is  the  mastoid  foramen  for 
the  passage  of  the  mastoid  emissary  vein. 

Norma  Frontalis  (Fig.  190).— When  viewed  from  the  front  the  skull  exhibits  a 
somewhat  oval  outline,  limited  above  by  the  frontal  bone,  belmv  by  the  body  of  the 
raandible,  and  laterally  by  the  zygomatic  bones  and  the  mandibular  rami.  The 
upper  part,  formed  by  the  frontal  squama,  is  smooth  and  convex.  The  lower  part, 
made  up  of  the  bones  of  the  face,  is  irregular;  it  is  excavated  laterally  by  the  orbital 
^cavities,  and  presents  in  the  middle  line  the  anterior  nasal  aperture  leading  to  the 


1  Occasionally  the  maxilla  and  the  sphenoid  articulate  with  each  other  at  the  anterior  extremity  of  this  fissure;  the 
sygomatic  is  then  excluded  from  it. 


■ 


186 


OSTEOLOGY 


nasal  cavities,  and  below  this  the  transverse  slit  between  the  upper  and  loAver 
dental  arcades.  Above,  the  frontal  eminences  stand  out  more  or  less  prominently, 
and  beneath  these  are  the  superciliary  arches,  joined  to  one  another  in  the  middle 
by  the  glabella.  On  and  above  the  glabella  a  trace  of  the  frontal  suture  sometimes 
persists;  beneath  it  is  the  frontonasal  suture,  the  mid-point  of  which  is  termed  the 
nasion.  Behind  and  below  the  frontonasal  suture  the  frontal  articulates  with  the 
frontal  process  of  the  maxilla  and  with  the  lacrimal.  Arching  transversely  below 
the  superciliary  arches  is  the  upper  part  of  the  margin  of  the  orbit,  thin  and  promi- 


Supraorbital  foramen 


Superior  orbital  fissure 

Lamina  papyracea  of  ethmoid 

Lacrimal 

Inferior  orbital  fissure 

Zygomaticofacial  foramen 

Irifraorhital  foramen 
Nasal  cavity 
Inferior  nasal  concha 


Mental  foratMti 


Fig.   190. — The  skull  from  the  front. 


nent  in  its  lateral  two-thirds,  rounded  in  its  medial  third,  and  presenting,  at  the 
junction  of  these  two  portions,  the  supraorbital  notch  or  foramen  for  the  supra- 
orbital nerve  and  vessels.  The  supraorbital  margin  ends  laterally  in  the  zygomatic 
process  which  articulates  w^ith  the  zygomatic  bone,  and  from  it  the  temporal  line 
extends  upward  and  backward.  Below  the  frontonasal  suture  is  the  bridge  of  the 
nose,  convex  from  side  to  side,  concavo-convex  from  above  downward,  and  formed 
by  the  two  nasal  bones  supported  in  the  middle  line  by  the  perpendicular  plate 
of  the  ethmoid,  and  laterally  by  the  frontal  processes  of  the  maxillae  which  are 
prolonged  upward  between  the  nasal  and  lacrimal  bones  and  form  the  lower  and 


THE  EXTERIOR  OF  THE  SKULL 


187 


medial  part  of  the  circumference  of  each  orbit.  Below  the  nasal  bones  and  between 
the  maxillae  is  the  anterior  aperture  of  the  nose,  pyriform  in  shape,  with  the  narrow 
end  directed  upward.  Laterally  this  opening  is  bounded  by  sharp  margins,  to 
\\hich  the  lateral  and  alar  cartilages  of  the  nose  are  attached;  below,  the  margins 
are  thicker  and  curve  medialward  and  forward  to  end  in  the  anterior  nasal  spine. 
On  looking  into  the  nasal  cavity,  the  bony  septum  which  separates  the  nasal 
cavities  presents,  in  front,  a  large  triangular  deficiency;  this,  in  the  fresh  state, 
is  filled  up  by  the  cartilage  of  the  nasal  septum;  on  the  lateral  wall  of  each  nasal 
cavity  the  anterior  part  of  the  inferior  nasal  concha  is  visible.  Below  and  lateral 
to  the  anterior  nasal  aperture  are  the  anterior  surfaces  of  the  maxillae,  each 
perforated,  near  the  lower  margin  of  the  orbit,  by  the  infraorbital  foramen  for  the 


Nasal  bone 


Lacrfmal  sulcus 

Zygomatic  hone 
Maxilla 


Ayit.  ethmoidal  cells 

Nasal  septum 

Probe  in 
infundibulum 
Middle  ethmmdal  cells 

Superior  nasal  concha 
~^ost.  ethmoidal  cells 
Superior  meatus 


Sphenoidal  sinuses 


Infraorbital  groove 


Inferior  orbital 
fissure 


Palatine  hone 


Sphenoidal  hone 
Foramen  rotundum 


Foramen  ovale 
Foramen  spinosum 


Carotid  canal 
Fig.  191. — Horizontal  section  of  nasal  and  orbital  cavities. 


[jJassage  of  the  infraorbital  nerve  and  vessels.  Below  and  medial  to  this  foramen 
is  the  canine  eminence  separating  the  incisive  from  the  canine  fossa.  Beneath 
piiese  fossae  are  the  alveolar  processes  of  the  maxillae  containing  the  upper  teeth, 
rhich  overlap  the  teeth  of  the  mandible  in  front.  The  zygomatic  bone  on  either 
^de  forms  the  prominence  of  the  cheek,  the  lower  and  lateral  portion  of  the  orbital 
lavity,  and  the  anterior  part  of  the  zj'gomatic  arch.  It  articulates  medially  with 
h;he  maxilla,  behind  with  the  zygomatic  process  of  the  temporal,  and  above  with 
me  great  wing  of  the  sphenoid  and  the  zygomatic  process  of  the  frontal;  it  is  per- 
lorated  by  the  zygomaticofacial  foramen  for  the  passage  of  the  zygomaticofacial 
Jierve.  On  the  body  of  the  mandible  is  a  median  ridge,  indicating  the  position 
of  the  symphysis;  this  ridge  divides  below  to  enclose  the  mental  protuberance,  the 
lateral  angles  of  which  constitute  the  mental  tubercles.     Below  the  incisor  teeth 


i 


188 


OSTEOLOGY 


is  the  incisive  fossa,  and  beneath  the  second  premolar  tooth  the  mental  foramen 
which  transmits  the  mental  nerve  and  vessels.  The  oblique  line  runs  upward  from 
the  mental  tubercle  and  is  continuous  behind  with  the  anterior  border  of  the  ramus. 
The  posterior  border  of  the  ramus  runs  downward  and  forward  from  the  condyle 
to  the  angle,  which  is  frequently  more  or  less  everted. 

The  Orbits  (orbitae)  (Fig.  190). — The  orbits  are  two  quadrilateral  pyramidal  cavi- 
ties, situated  at  the  upper  and  anterior  part  of  the  face,  their  bases  being  directed 
forward  and  lateralward,  and  their  apices  backward  and  medialward,  so  that  their 
long  axes,  if  continued  backward,  would  meet  over  the  body  of  the  sphenoid. 
Each  presents  for  examination  a  roof,  a  floor,  a  medial  and  a  lateral  wall,  a  base, 
and  an  apex. 


Anterior 
ethmoidal  foramen 


Posterior  ethmoidal  foramen 
Orbital  process  of  palatine 
Optic  foramen 

Splienopalatine  foramen 

Sella  turcica 
Prdie  in  foramen  rotundum 


Fossa  for 

lacrimal  sac 

Uncinate  process 
of  ethmoid, 
Openings  of 
maxillary  sinus 
Inferior  nasal 
concha 


Probe  in  pterygoid  canal 
-Prdbe  in  pterygopalatine  canal 

Palatine  bone 

Lateral  pterygoid  plate 


Pyramidal  process  of  palatine 


Fig.  192. — Medial  wall  of  left  orbit.     < 

The  roof  is  concave,  directed  downward,  and  slightly  forward,  and  formed  in 
front  by  the  orbital  plate  of  the  frontal;  behind  by  the  small  wing  of  the  sphenoid. 
It  presents  medially  the  trochlear  fovea  for  the  attachment  of  the  cartilaginous 
pulley  of  the  Obliquus  oculi  superior;  laterally,  the  lacrimal  fossa  for  the  lacrimal 
gland;  and  posteriorly,  the  suture  between  the  frontal  bone  and  the  small  wing 
of  the  sphenoid. 

The  floor  is  directed  upward  and  lateralward,  and  is  of  less  extent  than  the 
roof;  it  is  formed  chiefly  by  the  orbital  surface  of  the  maxilla;  in  front  and  laterally, 
by  the  orbital  process  of  the  zygomatic  bone,  and  behind  and  medially,  to  a  small 
extent,  by  the  orbital  process  of  the  palatine.  At  its  medial  angle  is  the  upper 
opening  of  the  nasolacrimal  canal,  immediately  to  the  lateral  side  of  which  is  a 
depression  for  the  origin  of  the  Obliquus  oculi  inferior.  On  its  lateral  part  is  the 
suture  between  the  maxilla  and  zygomatic  bone,  and  at  its  posterior  part  that 
between  the  maxilla  and  the  orbital  process  of  the  palatine.  Running  forward 
near  the  middle  of  the  floor  is  the  infraorbital  groove,  ending  in  front  in  the  infra- 
orbital canal  and  transmitting  the  infraorbital  nerve  and  vessels. 


i 


THE  INTERIOR  OF  THE  SKULL  189 


The  medial  wall  (P'ig.  192)  is  nearly  vertical,  and  is  formed  from  before  back- 
ward by  the  frontal  process  of  the  maxilla,  the  lacrimal,  the  lamina  papyracea 
of  the  ethmoid,  and  a  small  part  of  the  body  of  the  sphenoid  in  front  of  the  optic 
foramen.  Sometimes  the  sphenoidal  concha  forms  a  small  part  of  this  wall  (see 
page  152).  It  exhibits  three  vertical  sutures,  viz.,  the  lacrimomaxillary,  lacrimo- 
ethmoidal,  and  sphenoethmoidal.  In  front  is  seen  the  lacrimal  groove,  which  lodges 
the  lacrimal  sac,  and  behind  the  groove  is  the  posterior  lacrimal  crest,  from  which 
the  lacrimal  part  of  the  Orbicularis  oculi  arises.  At  the  junction  of  the  medial 
wall  and  the  roof  are  the  frontomaxillary,  frontolacrimal,  frontoethmoidal,  and 
sphenofrontal  sutures.  The  point  of  junction  of  the  anterior  border  of  the  lacrimal 
with  the  frontal  is  named  the  dacryon.  In  the  frontoethmoidal  suture  are  the 
anterior  and  posterior  ethmoidal  foramina,  the  former  transmitting  the  nasociliary 
nerve  and  anterior  ethmoidal  vessels,  the  latter  the  posterior  ethmoidal  nerve  and 
vessels. 

The  lateral  wall,  directed  medialward  and  forward,  is  formed  by  the  orbital 
process  of  the  zygomatic  and  the  orbital  surface  of  the  great  wing  of  the  sphenoid; 
these  are  united  by  the  sphenozygomatic  suture  which  terminates  below  at  the 
front  end  of  the  inferior  orbital  fissure.  On  the  orbital  process  of  the  zygomatic 
bone  are  the  orbital  tubercle  (Whitnall)  and  the  orifices  of  one  or  two  canals  which 
transmit  the  branches  of  the  zygomatic  nerve.  Between  the  roof  and  the  lateral 
wall,  near  the  apex  of  the  orbit,  is  the  superior  orbital  fissure.  Through  this  fissure 
the  oculomotor,  the  trochlear,  the  ophthalmic  division  of  the  trigeminal,  and  the 
al)ducent  nerves  enter  the  orbital  cavity,  also  some  filaments  from  the  cavernous 
plexus  of  the  sympathetic  and  the  orbital  branches  of  the  middle  meningeal  artery. 
Passing  backward  through  the  fissure  are  the  ophthalmic  vein  and  the  recurrent 
branch  from  the  lacrimal  artery  to  the  dura  mater.  The  lateral  wall  and  the  floor 
are  separated  posteriorly  by  the  inferior  orbital  fissure  which  transmits  the  maxillary 
nerve  and  its  zygomatic  branch,  the  infraorbital  vessels,  and  the  ascending  branches 
from  the  sphenopalatine  ganglion. 

The  base  of  the  orbit,  quadrilateral  in  shape,  is  formed  above  by  the  supra- 
orbital arch  of  the  frontal  bone,  in  which  is  the  supraorbital  notch  or  foramen  for 
tlie  passage  of  the  supraorbital  vessels  and  nerve;  below  by  the  zygomatic  bone  and 
maxilla,  united  by  the  zygomaticomaxillary  suture;  laterally  by  the  zygomatic 
bDne  and  the  zygomatic  process  of  the  frontal  joined  by  the  zygomaticofrontal 
suture;  medially  by  the  frontal  bone  and  the  frontal  process  of  the  maxilla  united 
by  the  frontomaxillary  suture. 

The  apex,  situated  at  the  back  of  the  orbit,  corresponds  to  the  optic  foramen^ 
a  short,  cylindrical  canal,  which  transmits  the  optic  nerve  and  ophthalmic  artery. 

It  will  thus  be  seen  that  there  are  nine  openings  communicating  with  each 
orbit,  viz.,  the  optic  foramen,  superior  and  inferior  orbital  fissures,  supraorbital 
foramen,  infraorbital  canal,  anterior  and  posterior  ethmoidal  foramina,  zygomatic 
foramen,  and  the  canal  for  the  nasolacrimal  duct. 

THE   INTERIOR   OF   THE    SKULL. 

Inner  Surface  of  the  Skull-cap. — The  inner  surface  of  the  skull-cap  is  concave 
and  presents  depressions  for  the  convolutions  of  the  cerebrum,  together  with 
numerous  furrows  for  the  lodgement  of  branches  of  the  meningeal  vessels.  Along 
tlie  middle  line  is  a  longitudinal  groove,  narrow  in  front,  where  it  commences  at 
the  frontal  crest,  but  broader  behind;  it  lodges  the  superior  sagittal  sinus,  and  its 
margins  afford  attachment  to  the  falx  cerebri.    On  either  side  of  it  are  several 

■  Some  anatomists  describe  the  apex  of  the  orbit  as  corresponding  with  the  medial  end  of  the  superior  orbital  fissure. 
It  seems  better,  however,  to  adopt  the  statement  in  the  text,  since  the  ocular  muscles  take  origin  around  the  optio 
foramen,  and  diverge  from  it  to  the  bulb  of  the  eye. 


■ 


190  OSTEOLOGY 


I 


depressions  for  the  arachnoid  granulations,  and  at  its  back  part,  the  openings  of 
the  parietal  foramina  when  these  are  present.  It  is  crossed,  in  front,  by  the  coronal 
suture,  and  behind  by  the  lambdoidal,  while  the  sagittal  lies  in  the  medial  plane 
between  the  parietal  bones. 

Upper  Surface  of  the  Base  of  the  Skull  (Fig.  19,3). — The  upper  surface  of  the 
base  of  the  skull  or  floor  of  the  cranial  cavity  presents  three  fossae,  called  the  anterior, 
middle,  and  posterior  cranial  fossae. 

Anterior  Fossa  (fossa  cranii  anterior).- — The  floor  of  the  anterior  fossa  is  formed 
by  the  orbital  plates  of  the  frontal,  the  cribriform  plate  of  the  ethmoid,  and  the 
small  wings  and  front  part  of  the  body  of  the  sphenoid ;  it  is  limited  behind  by  the 
posterior  borders  of  the  small  wings  of  the  sphenoid  and  by  the  anterior  margin 
of  the  chiasmatic  groove.  It  is  traversed  by  the  frontoethmoidal,  sphenoethmoidal, 
and  sphenofrontal  sutures.  Its  lateral  portions  roof  in  the  orbital  cavities  and  sup- 
port the  frontal  lobes  of  the  cerebrum;  they  are  convex  and  marked  by  depressions 
for  the  brain  convolutions,  and  grooves  for  branches  of  the  meningeal  vessels. 
The  central  portion  corresponds  with  the  roof  of  the  nasal  cavity,  and  is  markedly 
depressed  on  either  side  of  the  crista  galli.  It  presents,  in  and  near  the  median 
line,  from  before  backward,  the  commencement  of  the  frontal  crest  for  the  attach- 
ment of  the  falx  cerebri;  the  foramen  cecum,  between  the  frontal  bone  and  the  crista 
galli  of  the  ethmoid,  which  usually  transmits  a  small  vein  from  the  nasal  cavity 
to  the  superior  sagittal  sinus;  behind  the  foramen  cecum,  the  crista  galli,  the 
free  margin  of  which  affords  attachment  to  the  falx  cerebri;  on  either  side  of  the 
crista  galli,  the  olfactory  groove  formed  by  the  cribriform  plate,  which  supports 
the  olfactory  bulb  and  presents  foramina  for  the  transmission  of  the  olfactory 
nerves,  and  in  front  a  slit-like  opening  for  the  nasociliary  nerve.  Lateral  to  either 
olfactory  groove  are  the  internal  openings  of  the  anterior  and  posterior  ethmoidal 
foramina;  the  anterior,  situated  about  the  middle  of  the  lateral  margin  of  the  olfac- 
tory groove,  transmits  the  anterior  ethmoidal  vessels  and  the  nasociliary  nerve;  the 
nerve  runs  in  a  groove  along  the  lateral  edge  of  the  cribriform  plate  to  the  slit-like 
opening  above  mentioned;  the  posterior  ethmoidal  foramen  opens  at  the  back  part 
of  this  margin  under  cover  of  the  projecting  lamina  of  the  sphenoid,  and  transmits 
the  posterior  ethmoidal  vessels  and  nerve.  Farther  back  in  the  middle  line  is  the 
ethmoidal  spine,  bounded  behind  by  a  slight  elevation  separating  two  shallow  lon- 
gitudinal grooves  which  support  the  olfactory  lobes.  Behind  this  is  the  anterior 
margin  of  the  chiasmatic  groove,  running  lateralward  on  either  side  to  the  upper 
margin  of  the  optic  foramen. 

The  Middle  Fossa  (fossa  cranii  media). — The  middle  fossa,  deeper  than  the  pre- 
ceding, is  narrow  in  the  middle,  and  wide  at  the  sides  of  the  skull.  It  is  bounded 
in  front  by  the  posterior  margins  of  the  small  wings  of  the  sphenoid,  the  anterior 
clinoid  processes,  and  the  ridge  forming  the  anterior  margin  of  the  chiasmatic 
groove;  behind,  by  the  superior  angles  of  the  petrous  portions  of  the  temporals 
and  the  dorsum  sellse;  laterally  by  the  temporal  squamse,  sphenoidal  angles  of  the 
parietals,  and  great  wings  of  the  sphenoid.  It  is  traversed  by  the  squamosal, 
sphenoparietal,  sphenosquamosal,  and  sphenopetrosal  sutures. 

The  middle  part  of  the  fossa  presents,  in  front,  the  chiasmatic  groove  and  tuber- 
culum  sellse;  the  chiasmatic  groove  ends  on  either  side  at  the  optic  foramen,  which 
transmits  the  optic  nerve  and  ophthalmic  artery  to  the  orbital  cavity.  Behind 
the  optic  foramen  the  anterior  clinoid  process  is  directed  backward  and  medialward 
and  gives  attachment  to  the  tentorium  cerebelli.  Behind  the  tuberculum  sellae 
is  a  deep  depression,  the  sella  turcica,  containing  the  fossa  hypophyseos,  which  lodges 
the  hypophysis,  and  presents  on  its  anterior  wall  the  middle  clinoid  processes. 
The  sella  turcica  is  bounded  posteriori}^  by  a  quadrilateral  plate  of  bone,  the  dorsum 
sellse,  the  upper  angles  of  which  are  surmounted  by  the  posterior  clinoid  processes : 
these  afford  attachment  to  the  tentorium  cerebelli,  and  below  each  is  a  notch  for 


THE  INTERIOR  OF  THE  SKULL 


191 


the  abducent  nerve.    On  either  side  of  the  sella  turcica  is  the  carotid  groove,  which 
is  broad,  shallow,  and  curved  somewhat  like  the  italic  letter  /.    It  begins  behind 


Groove  for  super,  sagittal  sinus 

Grooves  for  anier.  meningeal  vessels 

Foramen  ccecum 

Crista  galli 

Slit  for  nasociliary  nerve 

Groove  for  nasociliary  nerve 

Anterior  ethmoidal  foramen 

Orifices  for  olfactory  nerves 
Posterior  ethmoidal  foramen 

Ethmoidal  spine 


Olfactory  grooves 

Optic  foramen 

Chiasmatic  groove 

Tubercidum  sellae 

Anterior  clinoid  process 

Middle  clinoid  process 

Posterior  clinoid  process 

Groove  for  abdiicent  nerve 

Foramen  lacerum 

Orifice  of  carotid  canal 

ssion  for  semilunar  ganglion 


Let 


tfJJepres 

■ 

I  ^^^K  Internal  acoustic  meatus 

I  ^^H  Slit  for  dura  mater 
I  ^^^R    Groove  for  superior  petrosal  sinus 

I  ^^B  Jugular  foramen 

I  ^^H  Hypoglossal  canal 

I  ^^^B  Aqucedticttis  vestibuli 

I^^H^  Condyloid  foramen, 

B 

I  ^^^^  Mastoid  foramen 

Posterior  meningeal  grooves 


I 


Fig.   193. — Base  of  the  skull.     Upper  surface. 


at  the  foramen  lacerum,  and  ends  on  the  medial  side  of  the  anterior  clinoid  process, 
where  it  is  sonietimes  converted  into  a  foramen  (carotico-clinoid)  by  the  union  of 
the  anterior  with  the  middle  clinoid  process;  posteriorly,  it  is  bounded  laterally 


192 


OSTEOLOGY 


I 


by  the  lingula.  This  groove  lodges  the  cavernous  sinus  and  the  internal  carc>tid 
artery,  the  latter  being  surrounded  by  a  plexus  of  sympathetic  nerves. 

The  lateral  parts  of  the  middle  fossa  are  of  considerable  depth,  and  support 
the  temporal  lobes  of  the  brain.  They  are  marked  by  depressions  for  the  brain 
convolutions  and  traversed  by  furrows  for  the  anterior  and  posterior  branches 
of  the  middle  meningeal  vessels.  These  furrows  begin  near  the  foramen  spinosiim, 
and  the  anterior  runs  forward  and  upward  to  the  sphenoidal  angle  of  the  parietal, 
where  it  is  sometimes  converted  into  a  bony  canal;  the  posterior  runs  lateral  ward 
and  backward  across  the  temporal  squama  and  passes  on  to  the  parietal  near 
the  middle  of  its  lower  border.  The  following  apertures  are  also  to  be  seen.  In 
front  is  the  superior  orbital  fissure,  bounded  above  by  the  small  wing,  below,  by  the 
great  wing,  and  medially,  by  the  body  of  the  sphenoid;  it  is  usually  completed 
laterally  by  the  orbital  plate  of  the  frontal  bone.  It  transmits  to  the  orbital 
cavity  the  oculomotor,  the  trochlear,  the  ophthalmic  division  of  the  trigeminal, 
and  the  abducent  nerves,  some  filaments  from  the  cavernous  plexus  of  the 
sympathetic,  and  the  orbital  branch  of  the  middle  meningeal  artery;  and  from  the 
orbital  cavity  a  recurrent  branch  from  the  lacrimal  artery  to  the  dura  mater,  and 
the  ophthalmic  veins.  Behind  the  medial  end  of  the  superior  orbital  fissure  is 
the  foramen  rotundum,  for  the  passage  of  the  maxillary  nerve.  Behind  and  lateral 
to  the  foramen  rotundum  is  the  foramen  ovale,  which  transmits  the  mandibular 
nerve,  the  accessory  meningeal  artery,  and  the  lesser  superficial  petrosal  nerve.^ 
Medial  to  the  foramen  ovale  is  the  foramen  Vesalii,  which  varies  in  size  in  different 
individuals,  and  is  often  absent;  when  present,  it  opens  below  at  the  lateral  side 
of  the  scaphoid  fossa,  and  transmits  a  small  vein.  Lateral  to  the  foramen  ovale 
is  the  foramen  spinosum,  for  the  passage  of  the  middle  meningeal  vessels,  and  a 
recurrent  branch  from  the  mandibular  nerve.  Medial  to  the  foramen  ovale  is 
the  foramen  lacerum;  in  the  fresh  state  the  lower  part  of  this  aperture  is  filled  up 
by  a  layer  of  fibrocartilage,  while  its  upper  and  inner  parts  transmit  the  internal 
carotid  artery  surrounded  by  a  plexus  of  sympathetic  nerves.  The  nerve  of  the 
pterygoid  canal  and  a  meningeal  branch  from  the  ascending  pharyngeal  artery 
pierce  the  layer  of  fibrocartilage.  On  the  anterior  surface  of  the  petrous  portion 
of  the  temporal  bone  are  seen  the  eminence  caused  by  the  projection  of  the  superior 
semicircular  canal;  in  front  of  and  a  little  lateral  to  this  a  depression  corresponding 
to  the  roof  of  the  tympanic  cavity;  the  groove  leading  to  the  hiatus  of  the  facial 
canal,  for  the  transmission  of  the  greater  superficial  petrosal  nerve  and  the  petrosal 
branch  of  the  middle  meningeal  artery ;  beneath  it,  the  smaller  groove,  for  the  pas- 
sage of  the  lesser  superficial  petrosal  nerve;  and,  near  the  apex  of  the  bone,  the 
depression  for  the  semilunar  ganglion  and  the  orifice  of  the  carotid  canal. 

The  Posterior  Fossa  (fossa  cranii  posterior). — -The  posterior  fossa  is  the  largest 
and  deepest  of  the  three.  It  is  formed  by  the  dorsum  sellse  and  clivus  of  the 
sphenoid,  the  occipital,  the  petrous  and  mastoid  portions  of  the  temporals,  and  the 
mastoid  angles  of  the  parietal  bones;  it  is  crossed  by  the  occipitomastoid  and  the 
parietomastoid  sutures,  and  lodges  the  cerebellum,  pons,  and  medulla  oblongata. 
It  is  separated  from  the  middle  fossa  in  and  near  the  median  line  by  the  dorsum 
sellse  of  the  sphenoid  and  on  either  side  by  the  superior  angle  of  the  petrous  por- 
tion of  the  temporal  bone.  This  angle  gives  attachment  to  the  tentorum  cerebelli, 
is  grooved  for  the  superior  petrosal  sinus,  and  presents  at  its  medial  end  a  notch 
upon  which  the  trigeminal  nerve  rests.  The  fossa  is  limited  behind  by  the  grooves 
for  the  transverse  sinuses.  In  its  center  is  the  foramen  magnum,  on  either  side  of 
which  is  a  rough  tubercle  for  the  attachment  of  the  alar  ligaments;  a  little  above 
this  tubercle  is  the  canal,  which  transmits  the  hypoglossal  nerve  and  a  meningeal 
branch  from  the  ascending  pharyngeal  artery.    In  front  of  the  foramen  magnum 


'  See  footnote,  page  150. 


THE  INTERIOR  OF  THE  SKULL 


193 


the  basilar  portion  of  the  occipital  and  the  posterior  part  of  the  body  of  the  sphenoid 
form  a  grooved  surface  which  supports  the  medulla  oblongata  and  pons;  in  the 
young  skull  these  bones  are  joined  by  a  synchondrosis.  This  grooved  surface  is 
separated  on  either  side  from  the  petrous  portion  of  the  temporal  by  the  petro- 
occipital  fissure,  which  is  occupied  in  the  fresh  state  by  a  plate  of  cartilage;  the 
fissure  is  continuous  behind  with  the  jugular  foramen,  and  its  margins  are  grooved 
for  the  inferior  petrosal  sinus.  The  jugular  foramen  is  situated  between  the  lateral 
part  of  the  occipital  and  the  petrous  part  of  the  temporal.  The  anterior  portion 
of  this  foramen  transmits  the  inferior  petrosal  sinus;  the  posterior  portion,  the 
transverse  sinus  and  some  meningeal  branches  from  the  occipital  and  ascending 
pharyngeal  arteries;  and  the  intermediate  portion,  the  glossopharyngeal,  vagus, 
and  accessory  nerves.  Above  the  jugular  foramen  is  the  internal  acoustic  meatus, 
for  the  facial  and  acoustic  nerves  and  internal  auditory  artery;  behind  and  lateral 


Palatine  bone 
Fig.  194. — Sagittal  section  of  skull. 

this  is  the  slit-like  opening  leading  into  the  aquseductus  vestibuli,  which  lodges 
the  ductus  endolymphaticus;  while  between  these,  and  near  the  superior  angle  of 
the  petrous  portion,  is  a  small  triangular  depression,  the  remains  of  the  fossa  sub- 
arcuata,  which  lodges  a  process  of  the  dura  mater  and  occasionally  transmits  a  small 
ivein.  Behind  the  foramen  magnum  are  the  inferior  occipital  fossae,  which  support 
the  hemispheres  of  the  cerebellum,  separated  from  one  another  by  the  internal 
occipital  crest,  which  serves  for  the  attachment  of  the  falx  cerebelli,  and  lodges 
the  occipital  sinus.  The  posterior  fossae  are  surmounted  by  the  deep  grooves  for 
the  transverse  sinuses.  Each  of  these  channels,  in  its  passage  to  the  jugular  foramen, 
grooves  the  occipital,  the  mastoid  angle  of  the  parietal,  the  mastoid  portion  of  the 
temporal,  and  the  jugular  process  of  the  occipital,  and  ends  at  the  back  part  of 
the  jugular  foramen.  Where  this  sinus  grooves  the  mastoid  portion  of  the  temporal, 
the  orifice  of  the  mastoid  foramen  may  be  seen;  and,  just  previous  to  its  termina- 
I  tion,  the  condyloid  canal  opens  into  it;  neither  opening  is  constant. 
13 


194 


OSTEOLOGY 


The  Nasal  Cavity  {camim.  nasi;  nasal  fossa). — The  nasal  cavities  are  two  irregu 
spaces,  situated  one  on  either  side  of  the  middle  line  of  the  face,  extending  from  the 
base  of  the  cranium  to  the  roof  of  the  mouth,  and  separated  from  each  other  by  a 
thin  vertical  septum.  They  open  on  the  face  through  the  pear-shaped  anterior  nasal 
aperture,  and  their  posterior  openings  or  choanse  communicate,  in  the  fresh 
state,  with  the  nasal  part  of  the  pharynx.  They  are  much  narrower  above  than 
below,  and  in  the  middle  than  at  their  anterior  or  posterior  openings:  their  depth, 
which  is  considerable,  is  greatest  in  the  middle.  They  communicate  with  the 
frontal,  ethmoidal,  sphenoidal,  and  maxillary  sinuses.  Each  cavity  is  bounded 
by  a  roof,  a  floor,  a  medial  and  a  lateral  wall. 

The  roof  (Figs.  195,  196)  is  horizontal  in  its  central  part,  but  slopes  do\An- 
ward  in  front  and  behind;  it  is  formed  in  front  by  the  nasal  bone  and  the  spine 
of  the  frontal;  in  the  middle,  by  the  cribriform  plate  of  the  ethmoid;  and  behind, 


Crest  of  nasal  hones 
Frontal  spine 


Space  for  triangular 
cartilage  of  septum 


Crest  of  palatines 
Crest  of  maxilla 


Fig.  195. — Medial  wall  of  left  nasal  fossa. 


by  the  body  of  the  sphenoid,  the  sphenoidal  concha,  the  ala  of  the  vomer  and  the 
sphenoidal  process  of  the  palatine  bone.  In  the  cribriform  plate  of  the  ethmoid 
are  the  foramina  for  the  olfactory  nerves,  and  on  the  posterior  part  of  the  roof 
is  the  opening  into  the  sphenoidal  sinus. 

The  floor  is  flattened  from  before  backward  and  concave  from  side  to  side. 
It  is  formed  by  the  palatine  process  of  the  maxilla  and  the  horizontal  part  of 
the  palatine  bone;  near  its  anterior  end  is  the  opening  of  the  incisive  canal. 

The  medial  wall  (septum  nasi)  (Fig.  195),  is  frequently  deflected  to  one  or  other 
side,  more  often  to  the  left  than  to  the  right.  It  is  formed,  in  front,  by  the  crest 
of  the  nasal  bones  and  frontal  spine;  in  the  middle,  by  the  perpendicular  plate 
of  the  ethmoid;  behind,  by  the  vomer  and  the  rostrum  of  the  sphenoid;  below, 
by  the  crest  of  the  maxillae  and  palatine  bones.  It  presents,  in  front,  a  large, 
triangular  notch,  which  receives  the  cartilage  of  the  septum;  and  behind,  the 
free  edge  of  the  vomer.     Its  surface  is  marked  by  numerous  furrows  for  vessels 


THE  INTERIOR  OF  THE  SKULL 


195 


and  nerves  and  by  the  grooves  for  the  nasopalatine  nerve,  and  is  traversed  by 
sutures  connecting  the  bones  of  which  it  is  formed. 

The  lateral  wall  (Fig.  196)  is  formed,  in  front,  by  the  frontal  process  of  the 
maxilla  and  by  the  lacrimal  bone;  in  the  middle,  by  the  ethmoid,  maxilla,  and 
inferior  nasal  concha;  behind,  by  the  vertical  plate  of  the  palatine  bone,  and  the 
medial  pterygoid  plate  of  the  sphenoid.  On  this  wall  are  three  irregular  antero- 
posterior passages,  termed  the  superior,  middle,  and  inferior  meatuses  of  the  nose. 
The  superior  meatus,  the  smallest  of  the  three,  occupies  the  middle  third  of  the 
lateral  wall.  It  lies  between  the  superior  and  middle  nasal  conchse;  the  spheno- 
palatine foramen  opens  into  it  behind,  and  the  posterior  ethmoidal  cells  in  front. 
The  sphenoidal  sinus  opens  into  a  recess,  the  sphenoethmoidal  recess,  which  is  placed 
above  and  behind  the  superior  concha.  The  middle  meatus  is  situated  between  the 
middle  and  inferior  conchse,  and  extends  from  the  anterior  to  the  posterior  end  of 


Nasal  bone 
Frontal  spine 


Cribriform  plate  of  ethmoid 
Sphenoid 


Probe  passed  through 
nasolacrimal  canal 

Bristle  passed  through 
infundibulum 


Frontal  prpe.  of  maxilla 

Lacrimal 

Ethmoid 

Uncinate  proc.  of  ethmoid 
Inferior  nasal  concha 
Palatine 

Superior  meatus 
Middle  meatus 
Inferior  meatus 


Anterior  nasal  spine 

Palatine  proc.  of  maxilla 

Ryrizontal  part  of  palatini 

Posterior  nasal  spine 

Incisive  canal- 


Fig.   196. — Roof,  floor,  and  lateral  wall  of  left  nasal  cavity. 


't,he  latter.  The  lateral  wall  of  this  meatus  can  be  satisfactorily  studied  only  after 
t;he  removal  of  the  middle  concha.  On  it  is  a  curved  fissure,  the  hiatus  semilunaris, 
limited  below  by  the  edge  of  the  uncinate  process  of  the  ethmoid  and  above  by 
an  elevation  named  the  bulla  ethmoidaUs;  the  middle  ethmoidal  cells  are  contained 
within  this  bulla  and  open  on  or  near  to  it.  Through  the  hiatus  semilunaris 
i:he  meatus  communicates  with  a  curved  passage  termed  the  infundibulum,  which 
<3ommunicates  in  front  with  the  anterior  ethmoidal  cells  and  in  rather  more  than 
Sfty  per  cent,  of  skulls  is  continued  upward  as  the  frontonasal  duct  into  the  frontal 
air-sinus;  when  this  continuity  fails,  the  frontonasal  duct  opens  directly  into  the 
anterior  part  of  the  meatus.  Below  the  bulla  ethmoidalis  and  hidden  by  the  unci- 
nate process  of  the  ethmoid  is  the  opening  of  the  maxillary  sinus  (ostium  maxillare) ; 
an  accessory  opening  is  frequently  present  above  the  posterior  part  of  the  inferior 
nasal  concha.  The  inferior  meatus,  the  largest  of  the  three,  is  the  space  between 
the  inferior  concha  and  the  floor  of  the  nasal  cavitv.    It  extends  almost  the  entire 


I 


196 


OSTEOLOGY 


length  of  the  lateral  wall  of  the  nose,  is  broader  in  front  than  behind,  and  presents 
anteriorly  the  lower  orifice  of  the  nasolacrimal  canal. 

The  Anterior  Nasal  Aperture  (Fig.  181)  is  a  heart-shaped  or  pyriform  opening, 
whose  long  axis  is  vertical,  and  narrow  end  upward;  in  the  recent  state  it  is  much 
contracted  by  the  lateral  and  alar  cartilages  of  the  nose.  It  is  bounded  above  by 
the  inferior  borders  of  the  nasal  bones;  laterally  by  the  thin,  sharp  margins  which 
separate  the  anterior  from  the  nasal  surfaces  of  the  maxillae;  and  below  by  the  same 
borders,  where  they  curve  medialward  to  join  each  other  at  the  anterior  nasal 
spine. 

The  choanse  are  each  bounded  above  by  the  under  surface  of  the  body  of  the 
sphenoid  and  ala  of  the  vomer;  below,  by  the  posterior  border  of  the  horizontal 
part  of  the  palatine  bone;  laterally,  by  the  medial  pterygoid  plate;  they  are 
separated  from  each  other  by  the  posterior  border  of  the  vomer. 


DIFFERENCES   IN   THE   SKULL   DUE   TO   AGE. 

At  birth  the  skull  is  large  in  proportion  to  the  other  parts  of  the  skeleton,  but  its  facial  portion 
is  small,  and  equals  only  about  one-eighth  of  the  bulk  of  the  cranium  as  compared  with  one-l?aK 
in  the  adult.    The  frontal  and  parietal  eminences  are  prominent,  and  the  greatest  width  of  the 

skull  is  at  the  level  of  the  latter;  on  the  other 
Frontal  fontanel  hand,  the  glabella,  superciliary  arches,  and 

mastoid  processes  are  not  developed.  Ossi- 
fication of  the  skuU  bones  is  not  completed, 
and  many  of  them,  e.  g.,  the  occipital,  temp- 
orals, sphenoid,  frontal,  and  mandible,  consist 
of  more  than  one  piece.  Unossified  mem- 
branous intervals,  termed  Jontanelles,  are  seen 
at  the  angles  of  the  parietal  bones;  these 
fontaneUes  are  six  in  number:  two,  an  ante- 
rior and  a  posterior,  are  situated  in  the  middle 
hne,  and  two,  an  antero-lateral  and  a  postero- 
lateral, on  either  side. 

The  anterior  or  bregmaiic  fontanelle  (Fig. 
197)  is  the  largest,  and  is  placed  at  the  junc- 
tion of  the  sagittal,  coronal,  and  frontal 
sutures;  it  is  lozenge-shaped,  and  measiu-es 
about  4  cm.  in  its  antero-posterior  and  2.5 
cm.  in  its  transverse  diameter.  The  posterior 
fontanelle  is  triangular  in  form  and  is  situated 
at  the  junction  of  the  sagittal  and  lambdoidal 
sutures.  The  lateral  fontaneUes  (Fig,  198)  are 
small,  irregular  in  shape,  and  correspond  re- 
spectively with  the  sphenoidal  and  mastoid 
angles  of  the  parietal  bones.  An  additional 
fontanelle  is  sometimes  seen  in  the  sagittal 
suture  at  the  region  of  the  obehon.  The 
fontaneUes  are  usually  closed  by  the  growth 
and  extension  of  the  bones  which  surround 
them,  but  sometimes  they  are  the  sites  of 
separate  ossific  centers  which  develop  into 
sutural  bones.  The  posterior  and  lateral  fon- 
taneUes are  obliterated  within  a  month  or  two  after  birth,  but  the  anterior  is  not  completely 
closed  until  about  the  middle  of  the  second  year. 

The  smallness  of  the  face  at  birth  is  mainly  accounted  for  by  the  rudimentary  condition  of 
the  maxillae  and  mandible,  the  non-eruption  of  the  teeth,  and  the  small  size  of  the  maxillary  air 
sinuses  and  nasal  cavities.  At  birth  the  nasal  cavities  He  almost  entirely  between  the  orbits,  and 
the  lower  border  of  the  anterior  nasal  aperture  is  only  a  httle  below  the  level  of  the  orbital  floor. 
With  the  eruption  of  the  deciduous  teeth  there  is  an  enlargement  of  the  face  and  jaws,  and  these 
changes  are  still  more  marked  after  the  second  dentition. 

The  skull  grows  rapidly  from  birth  to  the  seventh  year,  by  which  time  the  foramen  magnum 
and  petrous  parts  of  the  temporals  have  reached  their  full  size  and  the  orbital  cavities  are  only 
a  httle  smaller  than  those  of  the  adult.    Growth  is  slow  from  the  seventh  year  until  the  approach 


Occipital  fontanel 


FiQ.  197. — Skull  at  birth,  showing  frontal  and  occipital 
fonticuli. 


CRANIOLOGY 


197 


of  jjuberty,  when  a  second  period  of  activity  occurs :  this  results  in  an  increase  in  all  directions, 
but  it  is  especially  marked  in  the  frontal  and  facial  regions,  where  it  is  associated  with  the  develop- 
ment of  the  air  sinuses. 

Obhteration  of  the  sutures  of  the  vault  of  the  skull  takes  place  as  age  advances.  This  process 
may  commence  between  the  ages  of  thirty  and  forty,  and  is  first  seen  on  the  inner  surface,  and 
some  ten  years  later  on  the  outer  surface  of  the  skull.  The  dates  given  are,  however,  only  approxi- 
mate, as  it  is  impossible  to  state  with  anything  hke  accuracy  the  time  at  which  the  sutures  are 
closed.  Obhteration  usually  occurs  first  in  the  posterior  part  of  the  sagittal  suture,  next  in  the 
coron.  1,  and  then  in  the  lambdoidal. 

In  old  age  the  skull  generally  becomes  thinner  and  Ughter,  but  in  a  small  proportion  of  cases 
it  increases  in  thickness  and  weight,  owing  to  an  hypertrophy  of  the  inner  table.  The  most  strik- 
ing feature  of  the  old  skull  is  the  diminution  in  the  size  of  the  maxillaj  and  mandible  consequent 
on  the  loss  of  the  teeth  and  the  absorption  of  the  alveolar  processes.  This  is  associated  with  a 
marked  reduction  in  the  vertical  measurement  of  the  face  and  with  an  alteration  in  the  angles 
of  the  mandible. 


Frontal  fontanel 


Mastoid  fontanel 

Sphenoidal  fontanel 
Fia.  198. — Skull  at  birth,  showing  sphenoidal  and  mastoid  fonticuli. 


SEXUAL   DIFFERENCES   IN   THE  SKULL. 


^"  Until  the  age  of  puberty  there  is  Httle  difference  between  the  skull  of  the  female  and  that  of 
the  male.  The  skull  of  an  adult  female  is,  as  a  rule,  lighter  and  smaller,  and  its  cranial  capacity 
about  10  per  cent,  less,  than  that  of  the  male.  Its  walls  are  thinner  and  its  muscular  ridges  less 
st:ongly  marked;  the  glabella,  supercihary  arches,  and  mastoid  processes  are  less  prominent, 
aid  the  corresponding  air  sinuses  are  small  or  rudimentary.  The  upper  margin  of  the  orbit  is 
sharp,  the  forehead  vertical,  the  frontal  and  parietal  eminences  prominent,  and  the  vault  some- 
wiat  flattened.  The  contour  of  the  face  is  more  rounded,  the  facial  bones  are  smoother,  and  the 
maxillae  and  mandible  and  their  contained  teeth  smaller.  From  what  has  been  said  it  will  be  seen 
that  more  of  the  infantile  characteristics  are  retained  in  the  skull  of  the  adult  female  than  in  that 
of  the  adult  male.  A  well-marked  male  or  female  skull  can  easily  be  recognized  as  such,  but  in 
some  cases  the  respective  characteristics  are  so  indistinct  that  the  determination  of  the  sex  may 
hv  difficult  or  impossible. 

■  CRANIOLOGY. 

Skulls  vary  in  size  and  shape,  and  the  term  craniology  is  applied  to  the  study  of  these  varia- 
tions. The  capacity  of  the  cranial  cavity  constitutes  a  good  index  of  the  size  of  the  brain  which 
it  contained,  and  is  most  conveniently  arrived  at  by  fiUing  the  cavity  with  shot  and  measuring 
the  contents  in  a  graduated  vessel.  Skulls  may  be  classified  according  to  their  capacities  as 
follows: 

1.  Microcephalic,  with  a  capacity  of  less  than  1350  c.cm. — e.  g.,  those  of  native  Austrahans 
arid  Andaman  Islanders. 

2.  Mesocephalic,  with  a  capacity  of  from  1350  c.cm.  to  1450  c.cm. — e.  g.,  those  of  African 
negroes  and  Chinese. 

3    Megacephalic,  with  a  capacity  of  over  1450  c.cm. — e.  g.,  those  of  Europeans,  Japanese,  and 
ikimos. 


I 


198  OSTEOLOGY 

In  comparing  the  shape  of  one  skull  with  that  of  another  it  is  necessary  to  adopt  some  definite 
position  in  which  the  skulls  should  be  placed  during  the  process  of  examination.  They  should 
be  so  placed  that  a  line  carried  through  the  lower  margin  of  the  orbit  and  upper  margin  oi'  the 
external  acoustic  meatus  is  in  the  horizontal  plane.  The  norma?  of  one  skull  can  then  be  com- 
pared with  those  of  another,  and  the  differences  in  contour  and  surface  form  noted.  Further, 
it  is  necessary  that  the  various  linear  measurements  used  to  determine  the  shape  of  the  tikuU 
should  be  made  between  definite  and  easily  localized  points  on  its  surface.  The  principal  points 
may  be  divided  into  two  groups:    (1)  those  in  the  median  plane,  and  (2)  those  on  either  side  of  it. 

The  Points  in  the  Median  Plane  are  the: 

Mental  Point.    The  most  prominent  point  of  the  chin. 

Alveolar  Point  or  Prosthion.  The  central  point  of  the  anterior  margin  of  the  upper  alveolar 
arch. 

Subnasal  Point.  The  middle  of  the  lower  border  of  the  anterior  nasal  aperture,  at  the  l^ase 
of  the  anterior  nasal  spine. 

Nasion.     The  central  point  of  the  frontonasal  suture. 

Glabella.    The  point  in  the  middle  line  at  the  level  of  the  superciliary  arches. 

Ophryon.  The  point  in  the  middle  line  of  the  forehead  at  the  level  where  the  temporal  lines 
most  nearly  approach  each  other. 

Bregma.    The  meeting  point  of  the  coronal  and  sagittal  sutures. 

Obelion.    A  point  in  the  sagittal  suture  on  a  level  with  the  parietal  foramina. 

Lambda.    The  point  of  junction  of  the  sagittal  and  lambdoidal  sutures. 

Occipital  Point.    The  point  in  the  middle  line  of  the  occipital  bone  farthest  from  the  glabella. 

Inion.    The  external  occipital  protuberance. 

Opisthion.    The  mid-point  of  the  posterior  margin  of  the  foramen  magnum. 

Basion.    The  mid-point  of  the  anterior  margin  of  the  foramen  magnum. 

The  Points  on  Either  Side  of  the  Median  Plane  are  the: 

Gonion.    The  outer  margin  of  the  angle  of  the  mandible. 

Dacryon.  The  point  of  union  of  the  antero-superior  angle  of  the  lacrimal  with  the  frontal 
bone  and  the  frontal  process  of  the  maxilla. 

Stephanion.    The  point  where  the  temporal  line  intersects  the  coronal  suture. 

Pterion.  The  point  where  the  great  wing  of  the  sphenoid  joins  the  sphenoidal  angle  of  the 
parietal. 

Auricular  Point.    The  center  of  the  orifice  of  the  external  acoustic  meatus. 

Asterion.    The  point  of  meeting  of  the  lambdoidal,  mastooccipital,  and  mastoparietal  sutures. 

The  horizontal  circumference  of  the  cranium  is  measured  in  a  plane  passing  through  the  glabella 
(Turner)  or  the  ophryon  (Flower)  in  front,  and  the  occipital  point  behind;  it  averages  about 
50  cm.  in  the  female  and  52.5  cm.  in  the  male. 

The  occipitofrontal  or  longitudinal  arc  is  measm-ed  from  the  nasion  over  the  middle  line  of  the 
vertex  to  the  opisthion:  while  the  basinasal  length  is  the  distance  between  the  basion  and  the 
nasion.  These  two  measurements,  plus  the  antero-posterior  diameter  of  the  foramen  magnum, 
represent  the  vertical  circumference  of  the  cranium. 

The  length  is  measured  from  the  glabella  to  the  occipital  point,  while  the  breadth  or  greatest 

transverse  diameter  is  usually  found  near  the  external  acoustic  meatus.     The  proportion  of 

,  (breadth  X  100)  .  ,    ,  ,   ,.    .    ,  •    ,       ^  ^      ^., 

breadth  to  length  , -r is  termed  the  cephalic  index  or  index  of  breadth. 

The  height  is  usually  measured  from  the  basion  to  the  bregma,  and  the  proportion  of  height 

,    (height  X  100)  .  ,  .    ,       ,    .  ^,  .  ^ 

to  length  ,  — r, constitutes  the  vertical  or  height  index. 

length 

In  studying  the  face  the  principal  points  to  be  noticed  are  the  proportion  of  its  length  and 
breadth,  the  shape  of  the  orbits  and  of  the  anterior  nasal  aperture,  and  the  degree  of  projection 
of  the  jaws. 

The  length  of  the  face  may  be  measured  from  the  ophryon  or  nasion  to  the  chin,  or,  if  the  mandible 
be  wanting,  to  the  alveolar  point;  while  its  width  is  represented  by  the  distance  between  the 
zygomatic  arches.  By  comparing  the  length  with  the  width  of  the  face,  skulls  may  be  divided 
into  two  groups;  dolichofacial  or  leptoprosope  (long  faced)  and  brachy facial  or  chemoprosope  (short 
faced). 

The  orbital  index  signifies  the  proportion  which  the  orbital  height  bears  to  the  orbital  width, 
thus: 

orbital  height  X  100 

orbital  width 
The  nasal  index  expresses  the  proportion  which  the  width  of  the  anterior  nasal  aperture  bears 
to  the  height  of  the  nose,  the  latter  being  measured  from  the  nasion  to  the  lower  margin  of  the 
nasal  aperture,  thus: 

nasal  width  X  100 

nasal  height 


CRANIOLOGY 


199 


The  degree  of  projection  of  the  jaws  is  determined  by  the  gnathic  or  alveolar  index,  which  repre- 
sents the  proportion  between  the  basialveolar  and  basinasal  lengths,  thus: 

basialveolar  length  X  100 
basinasal  length 
The  following  table,  modified  from  that  given  by  Duckworth, i  illustrates  how  these  different 
indices  may  be  utilized  in  the  classification  of  skuUs: 


Index. 

Classification. 

Nomenclature. 

Examples. 

1.  Cephahc 

Below  75 

Between  75  and  80 
Above  80 

Dolichocephalic 

Mesaticephalic 

BrachycephaUc 

Microseme 

Mesoseme 
Megaseme 

Leptorhine 
Mesorhine 
Platyrhine 

Orthognathous 
Mesognathous 
Prognathous 

Kaffirs  and  Native  Australians. 
Europeans  and  Chinese. 
Mongolians  and  Andamans. 

2.  Orbital 

Below  84 

Between  84  and  89 
Above  89 

Tasmanians  and  Native  Austra- 
lians. 
Europeans. 
Chinese  and  Polynesians. 

8.  Nasal 

P 

ft.  Gnathic 

Below  48 

Between  48  and  53 
Above  53 

Below  98 

Between  98  and  103 

Above  103 

Europeans. 

Japanese  and  Chinese. 

Negroes  and  Native  Australians. 

Europeans. 

Chinese  and  Japanese. 

Native  Australians. 

The  chief  function  of  the  skull  is  to  protect  the  brain,  and  therefore  those  portions  of  the  skull 
\7hich  are  most  exposed  to  external  violence  are  thicker  than  those  which  are  shielded  from  injury 
by  overlying  muscles.  Thus,  the  skull-cap  is  thick  and  dense,  whereas  the  temporal  squamae, 
being  protected  by  the  temporales  muscles,  and  the  inferior  occipital  fossa;,  being  shielded  by  the 
muscles  at  the  back  of  the  neck,  are  thin  and  fragile.  Fracture  of  the  skull  is  further  prevented 
by  its  elasticity,  its  rounded  shape,  and  its  construction  of  a  number  of  secondary  elastic  arches, 
each  made  up  of  a  single  bone.  The  manner  in  which  vibrations  are  transmitted  through  the 
bones  of  the  skull  is  also  of  importance  as  regards  its  protective  mechanism,  at  all  events  as  far 
JLS  the  base  is  concerned.  In  the  vault,  the  bones  being  of  a  fairly  equal  thickness  and  density, 
vibrations  are  transmitted  in  a  uniform  manner  in  all  directions,  but  in  the  base,  owing  to  the 
varying  thickness  and  density  of  the  bones,  this  is  not  so;  and  therefore  in  this  situation  there 
are  special  buttresses  which  serve  to  carry  the  vibrations  in  certain  definite  directions.  At  the 
iront  of  the  skull,  on  either  side,  is  the  ridge  which  separates  the  anterior  from  the  middle  fossa 
of  the  base;  and  behind,  the  ridge  or  buttress  which  separates  the  middle  from  the  posterior  fossa; 
and  if  any  violence  is  appHed  to  the  vault,  the  vibrations  would  be  carried  along  these  buttresses 
io  the  sella  turcica,  where  they  meet.  This  part  has  been  termed  the  "center  of  resistance," 
and  here  there  is  a  special  protective  mechanism  to  guard  the  brain.  The  subarachnoid  cavity 
at  the  base  of  the  brain  is  dilated,  and  the  cerebrospinal  fluid  which  fills  it  acts  as  a  water  cushion 
1.0  shield  the  brain  from  injury.  In  hke  manner,  when  violence  is  applied  to  the  base  of  the  skull, 
as  in  falls  upon  the  feet,  the  vibrations  are  carried  backward  through  the  occipital  crest,  and 
i  orward  through  the  basilar  part  of  the  occipital  and  body  of  the  sphenoid  to  the  vault  of  the  skull. 
In  connection  with  the  bones  of  the  face  a  common  malformation  is  cleft  palate.  The  cleft 
usually  starts  posteriorly,  and  its  most  elementary  form  is  a  bifid  uvula;  or  the  cleft  may  extend 
ihrough  the  soft  palate;  or  the  posterior  part  of  the  whole 
i)f  the  hard  palate  may  be  involved,  the  cleft  extending  as 
:'ar  forward  as  the  incisive  foramen.  In  the  severest  forms, 
:he  cleft  extends  through  the  alveolus  and  passes  between 
;he  incisive  or  premaxillary  bone  and  the  rest  of  the  max- 
-11a;  that  is  to  say,  between  the  lateral  incisor  and  canine 
^eeth.  In  some  instances,  the  cleft  runs  between  the  central 
and  lateral  incisor  teeth;  and  this  has  induced  some 
anatomists  to  beheve  that  the  premaxillary  bone  is  devel- 
oped from  two  centers  (Fig.  199)  and  not  from  one,  as  was 
stated  on  p.  163.  The  medial  segment,  bearing  a  central 
incisor,  is  called  an  endognathion;  the  lateral  segment,  bear- 
ing the  lateral  incisor,  is  called  a  mesognathion.  The  cleft 
may  affect  one  or  both  sides;  if  the  latter,  the  central  part  is  frequently  displaced  forward  and  re- 
^ mains  united  to  the  septum  of  the  nose,  the  deficiency  in  the  alveolus  being  complicated  with  a  cleft 

'  Morphology  and  Anthropology,  by  W.  L.  H.  Duckworth.  M.A.,  Cambridge  University  Press. 


Endognathion 
Mesognathion 
Exognathion 


Fig.  199.- 


-The  premaxilla  and  its  sutures. 
(After  Albrecht.) 


200  ^^^^^^^         OSTEOLOGY 


I 


in  the  lip  (hare-lip).  On  examining  a  cleft  palate  in  which  the  alveolus  is  not  implicated,  the  cleft 
will  generally  appear  to  be  in  the  median  line,  but  occasionally  is  unilateral  and  in  some  cases  bilat- 
eral. To  understand  this  it  must  be  borne  in  mind  that  three  processes  are  concerned  in  the  format  ion 
of  the  palate — the  palatine  processes  of  the  two  maxillse,  which  grow  in  horizontally  and  unite 
in  the  middle  line,  and  the  ethmovomerine  process,  which  grows  downward  from  the  base  of 
the  skull  and  frontonasal  process  to  unite  with  the  palatine  processes  in  the  middle  line.  In 
those  cases  where  the  palatine  processes  fail  to  unite  with  each  other  and  with  the  medial  process, 
the  cleft  of  the  palate  is  median;  where  one  palatine  process  unites  with  the  medial  septum,  the 
other  faiUng  to  do  so,  the  cleft  in  the  palate  is  unilateral.  In  some  cases  where  the  palatine  pro- 
cesses fail  to  meet  in  the  middle,  the  ethmovomerine  process  grows  downward  between  them  and 
thus  produces  a  bilateral  cleft.  Occasionally  there  may  be  a  hole  in  the  middle  line  of  the  hard 
palate,  the  anterior  part  of  the  hard  and  the  soft  palate  being  perfect;  this  is  rare,  because,  as 
a  rule,  the  union  of  the  various  processes  progresses  from  before  backward,  and  therefore  the 
posterior  part  of  the  palate  is  more  frequently  defective  than  the  anterior. 

THE   EXTREMITIES. 

The  bones  by  which  the  upper  and  lower  limbs  are  attached  to  the  trunk  con- 
stitute respectively  the  shoulder  and  pelvic  girdles.  The  shoulder  girdle  or  girdle 
of  the  superior  extremity  is  formed  by  the  scapulae  and  clavicles,  and  is  imperfect 
in  front  and  behind.  In  front,  however,  it  is  completed  by  the  upper  end  of  the 
sternum,  with  which  the  medial  ends  of  the  clavicles  articulate.  Behind,  it  is 
widely  imperfect,  the  scapulae  being  connected  to  the  trunk  by  muscles  only. 
The  pelvic  girdle  or  girdle  of  the  inferior  extremity  is  formed  by  the  hip  bones, 
which  articulate  with  each  other  in  front,  at  the  symphysis  pubis.  It  is  imperfect 
behind,  but  the  gap  is  filled  in  by  the  upper  part  of  the  sacrum.  The  pelvic  girdle, 
with  the  sacrum,  is  a  complete  ring,  massive  and  comparatively  rigid,  in  marked 
contrast  to  the  lightness  and  mobility  of  the  shoulder  girdle. 

THE  BONES  OF  THE  UPPER  EXTREMITY  (OSS A  EXTREMITATIS  SUPERIORIS). 

The  Clavicle  (Clavicula;  Collar  Bone). 

The  clavicle  (Figs.  200,  201)  forms  the  anterior  portion  of  the  shoulder  girdle. 
It  is  a  long  bone,  curved  somewhat  like  the  italic  letter/,  and  placed  nearly  horizon- 
tally at  the  upper  and  anterior  part  of  the  thorax,  immediately  above  the  first 
rib.  It  articulates  medially  with  the  manubrium  sterni,  and  laterally  with  the 
acromion  of  the  scapula.^  It  presents  a  double  curvature,  the  convexity  being 
directed  forward  at  the  sternal  end,  and  the  concavity  at  the  scapular  end.  Its 
lateral  third  is  flattened  from  above  downward,  while  its  medial  two-thirds  is  of 
a  rounded  or  prismatic  form. 

Lateral  Third. — The  lateral  third  has  two  surfaces,  an  upper  and  a  lower;  and 
two  borders,  an  anterior  and  a  posterior. 

Surface.^ — The  upper  surface  is  flat,  rough,  and  marked  by  impressions  for  the 
attachments  of  the  Deltoideus  in  front,  and  the  Trapezius  behind;  between  these 
impressions  a  small  portion  of  the  bone  is  subcutaneous.  The  under  surface  is 
flat.  At  its  posterior  border,  near  the  point  where  the  prismatic  joins  with  the 
flattened  portion,  is  a  rough  eminence,  the  coracoid  tuberosity  {conoid  tubercle)', 
this,  in  the  natural  position  of  the  bone,  surmounts  the  coracoid  process  of  the 
scapula,  and  gives  attachment  to  the  conoid  ligament.  From  this  tuberosity  an 
oblique  ridge,  the  oblique  or  trapezoid  ridge,  runs  forward  and  lateralward,  and 
afford  attachment  to  the  trapezoid  ligament. 

'  The  clavicle  acts  especially  as  a  fulcrum  to  enable  the  muscles  to  give  lateral  motion  to  the  arm.  It  is  accordingly 
absent  in  those  animals  whose  fore-limbs  are  used  only  for  progression,  but  is  present  for  the  most  part  in  animals 
whose  anterior  extremities  are  clawed  and  used  for  prehension,  though  in  some  of  them — as,  for  instance,  in  a  large 
number  of  the  carnivora — it  is  merely  a  rudimentary  bone  suspended  among  the  muscles,  and  not  articulating  with 
(either  the  scapula  or  sternum. 


THE 


[VI CLE 


Borders. — The  anterior  border  is  concave,  thin,  and  rough,  and  gives  attachment 
to  the  Deltoideus.  The  posterior  border  is  convex,  rough,  thicker  than  the  anterior, 
and  gives  attachment  to  the  Trapezius. 

Medial  Two-thirds. — The  medial  two-thirds  constitute  the  prismatic  portion 
of  the  bone,  which  is  curved  so  as  to  be  convex  in  front,  concave  behind,  and  is 
marked  by  three  borders,  separating  three  surfaces. 

Borders.^ — The  anterior  border  is  continuous  with  the  anterior  margin  of  the  flat 
portion.  Its  lateral  part  is  smooth,  and  corresponds  to  the  interval  between  the 
attachments  of  the  Pectoralis  major  and  Deltoideus;  its  medial  part  forms  the 
lower  boundary  of  an  elliptical  surface  for  the  attachment  of  the  clavicular  portion 


Sternal  extremity 


Acromial  extremity 


Fig.  200. — Left  clavicle.      Superior  surface. 

of  the  Pectoralis  major,  and  approaches  the  posterior  border  of  the  bone.  The 
superior  border  is  continuous  with  the  posterior  margin  of  the  flat  portion,  and 
separates  the  anterior  from  the  posterior  surface.  Smooth  and  rounded  laterally, 
it  becomes  rough  toward  the  medial  third  for  the  attachment  of  the  Sternocleido- 
raastoideus,  and  ends  at  the  upper  angle  of  the  sternal  extremity.  The  posterior 
or  subclavian  border  separates  the  posterior  from  the  inferior  surface,  and  extends 
from  the  coracoid  tuberosity  to  the  costal  tuberosity;  it  forms  the  posterior  boun- 
dary of  the  groove  for  the  Subclavius,  and  gives  attachment  to  a  layer  of  cervical 
lascia  which  envelops  the  Omohyoideus. 


Articular  capsule 


Inferior  surface. 

Surfaces. — The  anterior  surface  is  included  between  the  superior  and  anterior 
borders.  Its  lateral  part  looks  upward,  and  is  continuous  with  the  superior  sur- 
face of  the  flattened  portion;  it  is  smooth,  convex,  and  nearly  subcutaneous,  being 
covered  only  by  the  Platysma.  Medially  it  is  divided  by  a  narrow  subcutaneous 
area  into  two  parts!  a  lower,  elliptical  in  form,  and  directed  forward,  for  the 
attachment  of  the  Pectoralis  major;  and  an  upper  for  the  attachment  of  the 
Sternocleidomastoideus.  The  posterior  or  cervical  surface  is  smooth,  and  looks 
backward  toward  the  root  of  the  neck.  It  is  limited,  above,  by  the  superior 
border;  below,  by  the  subclavian  border;  medially,  by  the  margin  of  the  sternal 
extremity ;  and  laterally,  by  the  coracoid  tuberosity.    It  is  concave  medio-laterally, 


I 


202  OSTEOLOGY 


■I 


and  is  in  relation,  by  its  lower  part,  with  the  transverse  scapular  vessels.  This 
surface,  at  the  junction  of  the  curves  of  the  bone,  is  also  in  relation  with  the  brachial 
plexus  of  nerves  and  the  subclavian  vessels.  It  gives  attachment,  near  the  sternal 
extremity,  to  part  of  the  Sternohyoideus;  and  presents,  near  the  middle,  an  obliciue 
foramen  directed  lateralward,  which  transmits  the  chief  nutrient  artery  of  the 
bone.  Sometimes  there  are  two  foramina  on  the  posterior  surface,  or  one  on  the 
posterior  and  another  on  the  inferior  surface.  The  inferior  or  subclavian  surface  is 
bounded,  in  front,  by  the  anterior  border;  behind,  by  the  subclavian  border. 
It  is  narrowed  medially,  but  gradually  increases  in  width  laterally,  and  is  contin- 
uous with  the  under  surface  of  the  flat  portion.  On  its  medial  part  is  a  broad 
rough  surface,  the  costal  tuberosity  {rhomboid  impression),  rather  more  than  2  cm. 
in  length,  for  the  attachment  of  the  costoclavicular  ligament.  The  rest  of  this 
surface  is  occupied  by  a  groove,  which  gives  attachment  to  the  Subclavius;  the 
coracoclavicular  fascia,  which  splits  to  enclose  the  muscle,  is  attached  to  the  margins 
of  the  groove.  Not  infrequently  this  groove  is  subdivided  longitudinally  by  a 
line  which  gives  attachment  to  the  intermuscular  septum  of  the  Subclavius. 

The  Sternal  Extremity  {extremitas  sternalis;  internal  extremity). — The  sternal 
extremity  of  the  clavicle  is  triangular  in  form,  directed  medialward,  and  a  little 
downward  and  forward;  it  presents  an  articular  facet,  concave  from  before  back- 
ward, convex  from  above  downward,  which  articulates  with  the  manubrium  sterni 
through  the  intervention  of  an  articular  disk.  The  lower  part  of  the  facet  is  con- 
tinued on  to  the  inferior  surface  of  the  bone  as  a  small  semi-oval  area  for  articula- 
tion with  the  cartilage  of  the  first  rib.  The  circumference  of  the  articular  surface 
is  rough,  for  the  attachment  of  numerous  ligaments;  the  upper  angle  gives  attach- 
ment to  the  articular  disk. 

The  Acromial  Extremity  (extremitas  acromialis;  outer  extremity). — The  acromial 
extremity  presents  a  small,  flattened,  oval  surface  directed  obliquely  downward, 
for  articulation  with  the  acromion  of  the  scapula.  The  circumference  of  the 
articular  facet  is  rough,  especially  above,  for  the  attachment  of  the  acromio- 
clavicular ligaments. 

In  the  female,  the  clavicle  is  generally  shorter,  thinner,  less  curved,  and  smoother  than  in  the 
male.  In  those  persons  who  perform  considerable  manual  labor  it  becomes  thicker  and  more 
curved,  and  its  ridges  for  muscular  attachment  are  prominently  marked. 

Structure. — The  clavicle  consists  of  cancellous  tissue,  enveloped  by  a  compact  layer,  which 
is  much  thicker  in  the  intermediate  part  than  at  the  extremities  of  the  bone. 

Ossification. — The  clavicle  begins  to  ossify  before  any  other  bone  in  the  body;  it  is  ossified 
from  three  centers — viz.,  two  primary  centers,  a  medial  and  a  lateral,  for  the  body,i  which  appear 
during  the  fifth  or  sixth  week  of  fetal  Ufe;  and  a  secondary  center  for  the  sternal  end,  which 
appears  about  the  eighteenth  or  twentieth  year,  and  imites  with  the  rest  of  the  bone  about  the 
twenty-fifth  year. 

The  Scapula  (Shoulder  Blade). 

The  scapula  forms  the  posterior  part  of  the  shoulder  girdle.  It  is  a  flat,  trian- 
gular bone,  with  two  surfaces,  three  borders,  and  three  angles. 

Surfaces. — The  costal  or  ventral  surface  (Fig.  202)  presents  a  broad  concavity, 
the  subscapular  fossa.  The  medial  two-thirds  of  the  fossa  are  marked  by  several 
oblique  ridges,  which  run  lateralward  and  upward.  The  ridges  give  attachment 
to  the  tendinous  insertions,  and  the  surfaces  between  them  to  the  fleshy  fibers, 
of  the  Subscapularis.  The  lateral  third  of  the  fossa  is  smooth  and  covered  by  the 
fibers  of  this  muscle.  The  fossa  is  separated  from  the  vertebral  border  by  smooth 
triangular'  areas  at  the  medial  and  inferior  angles,  and  in  the  interval  between 
these  by  a  narrow  ridge  which  is  often  deficient.  These  triangular  areas  and  the 
intervening  ridge  afford  attachment  to  the  Serratus  anterior.  At  the  upper  part 
of  the  fossa  is  a  transverse  depression,  where  the  bone  appears  to  be  bent  on  itself 

1  Mall,  American  Journal  of  Anatomy,  vol.  v;  Fawcett,  Journal  of  Anatomy  and  Physiology,  vol.  xlvii. 


* 


I 


THE  SCAPULA  flHJHK  ^^^ 

along  a  line  at  right  angles  to  and  passing  through  the  center  of  the  glenoid  cavity, 
forming  a  considerable  angle,  called  the  subscapular  angle;  this  gives  greater 
strength  to  the  body  of  the  bone  by  its  arched  form,  while  the  summit  of  the 
arch  serves  to  support  the  spine  and  acromion. 

The  dorsal  surface  (Fig.  203)  is  arched  from  above  downward,  and  is  subdivided 
into  two  unequal  parts  by  the  spine;  the  portion  above  the  spine  is  called  the 
supraspinatous  fossa,  and  that  below  it  the  infraspinatous  fossa. 

The  supraspinatous  fossa,  the  smaller  of  the  two,  is  concave,  smooth,  and  broader 
at  its  vertebral  than  at  its  humeral  end;  its  medial  two-thirds  give  origin  to  the 
Supraspinatus. 

The  infraspinatous  fossa  is  much  larger  than  the  preceding;  toward  its  vertebral 
margin  a  shallow  concavity  is  seen  at  its  upper  part ;  its  center  presents  a  promi- 
nent convexity,  while  near  the  axillary  border  is  a  deep  groove  which  runs  from 
the  upper  toward  the  lower  part.  The  medial  two-thirds  of  the  fossa  give  origin 
to  the  Infraspinatus;  the  lateral  third  is  covered  by  this  muscle. 

The  dorsal  surface  is  marked  near  the  axillary  border  by  an  elevated  ridge, 
which  runs  from  the  lower  part  of  the  glenoid  cavity,  downward  and  backward 
to  the  vertebral  border,  about  2.5  cm.  above  the  inferior  angle.  The  ridge  serves 
for  the  attachment  of  a  fibrous  septum,  which  separates  the  Infraspinatus  from 
the  Teres  major  and  Teres  minor.  The  surface  between  the  ridge  and  the  axillary 
border  is  narrow  in  the  upper  two-thirds  of  its  extent,  and  is  crossed  near  its 
center  by  a  groove  for  the  passage  of  the  scapular  circumflex  vessels;  it  affords 
attachment  to  the  Teres  minor.  Its  lower  third  presents  a  broader,  somewhat 
triangular  surface,  which  gives  origin  to  the  Teres  major,  and  over  which  the  Latis- 
simus  dorsi  glides;  frequently  the  latter  muscle  takes  origin  by  a  few  fibers  from 
this  part.  The  broad  and  narrow  portions  above  alluded  to  are  separated  by  an 
oblique  line,  which  runs  from  the  axillary  border,  downward  and  backward,  to 
meet  the  elevated  ridge:  to  it  is  attached  a  fibrous  septum  which  separates  the 
Teres  muscles  from  each  other. 

The  Spine  (spina  scapuloB). — The  spine  is  a  prominent  plate  of  bone,  which 
crosses  obliquely  the  medial  four-fifths  of  the  dorsal  surface  of  the  scapula  at  its 
upper  part,  and  separates  the  supra-  from  the  infraspinatous  fossa.  It  begins 
at  the  vertical  border  by  a  smooth,  triangular  area  over  which  the  tendon  of  inser- 
tion of  the  lower  part  of  the  Trapezius  glides,  and,  gradually  becoming  more  ele- 
vated, ends  in  the  acromion,  which  overhangs  the  shoulder-joint.  The  spine  is 
triangular,  and  flattened  from  above  downward,  its  apex  being  directed  toward 
the  vertebral  border.  It  presents  two  surfaces  and  three  borders.  Its  superior 
surface  is  concave;  it  assits  in  forming  the  supraspinatous  fossa,  and  gives  origin 
to  part  of  the  Supraspinatus.  Its  inferior  surface  forms  part  of  the  infraspinatous 
fossa,  gives  origin  to  a  portion  of  the  Infraspinatus,  and  presents  near  its  center 
the  orifice  of  a  nutrient  canal.  Of  the  three  borders,  the  anterior  is  attached  to  the 
dorsal  surface  of  the  bone;  the  posterior,  or  crest  of  the  spine,  is  broad,  and  presents 
two  lips  and  an  intervening  rough  interval.  The  Trapezius  is  attached  to  the  supe- 
rior lip,  and  a  rough  tubercle  is  generally  seen  on  that  portion  of  the  spine  which 
receives  the  tendon  of  insertion  of  the  lower  part  of  this  muscle.  The  Deltoideus 
is  attached  to  the  whole  length  of  the  inferior  lip.  The  interval  between  the  lips 
is  subcutaneous  and  partly  covered  by  the  tendinous  fibers  of  these  muscles.  The 
lateral  border,  or  base,  the  shortest  of  the  three,  is  slightly  concave;  its  edge,  thick 
and  round,  is  continuous  above  with  the  under  surface  of  the  acromion,  below 
with  the  neck  of  the  scapula.  It  forms  the  medial  boundary  of  the  great  scapular 
notch,  which  serves  to  connect  the  supra-  and  infraspinatous  fossae. 

The  Acromion. — The  acromion  forms  the  summit  of  the  shoulder,  and  is  a  large, 
somewhat  triangular  or  oblong  process,  flattened  from  behind  forward,  projecting 
at  first  lateralward,  and  then  curving  forward  and  upward,  so  as  to  overhang  the 


204 


OSTEOLOGY 


glenoid  cavity.  Its  superior  surface,  directed  upward,  backward,  and  lateral war( 
is  convex,  rough,  and  gives  attachment  to  some  fibers  of  the  Deltoideus,  and  in  the 
rest  of  its  extent  is  subcutaneous.  Its  inferior  surface  is  smooth  and  conca\'e. 
Its  lateral  border  is  thick  and  irregular,  and  presents  three  or  four  tubercles  for  the 
tendinous  origins  of  the  Deltoideus.  Its  medial  border,  shorter  than  the  lateral, 
is  concave,  gives  attachment  to  a  portion  of  the  Trapezius,  and  presents  about 
its  center  a  small,  oval  surface  for  articulation  with  the  acromial  end  of  the  clavicle. 


Articular  capsule 


Coracoacromial  _L_li 

ligament 


rticular 
capsule 


Fig.  202. — Left  scapula.     Costal  surface. 


Its  apex,  which  corresponds  to  the  point  of  meeting  of  these  two  borders  in  front, 
is  thin,  and  has  attached  to  it  the  coracoacromial  ligament. 

Borders. — Of  the  three  borders  of  the  scapula,  the  superior  is  the  shortest  and 
thinnest;  it  is  concave,  and  extends  from  the  medial  angle  to  the  base  of  the  cora- 
coid  process.    At  its  lateral  part  is  a  deep,  semicircular  notch,  the  scapular  notch, 


THE  SCAPULA 


205 


formed  partly  by  the  base  of  the  coraeoid  process.  This  notch  is  converted  into 
a  foramen  by  the  superior  transverse  Hgament,  and  serves  for  the"  passage  of  the 
suprascapular  nerve;  sometimes  the  ligament  is  ossified.  The  adjacent  part  of 
the  superior  border  affords  attachment  to  the  Omohyoideus.    The  axillary  border 


Coracohumeral 
ligament 


Coraco-acromial  ligament 


^«Co 


Trapezoid  ligament 


Conoid  ligament 


FiQ.  203. — Left  scapula.     Dorsal  surface. 


I 


is  the  thickest  of  the  three.  It  begins  above  at  the  lower  margin  of  the  glenoid 
:avity,  and  inclines  obliquely  downward  and  backward  to  the  inferior  angle. 
Immediately  below  the  glenoid  cavity  is  a  rough  impression,  the  infraglenoid 
tuberosity,  about  2.5  cm.  in  length,  which  gives  origin  to  the  long  head  of  the  Tri- 
ceps brachii;  in  front  of  this  is  a  longitudinal  groove,  which  extends  as  far  as  the 


206 


OSTEOLOGY 


lower  third  of  this  border,. and  affords  origin  to  part  of  the  Subscapularis.  The 
inferior  third  is  thin  and  sharp,  and  serves  for  the  attachment  of  a  few  fibers  of 
the  Teres  major  behind,  and  of  the  Subscapularis  in  front.  The  vertebral  border 
is  the  longest  of  the  three,  and  extends  from  the  medial  to  the  inferior  angle.  It 
is  arched,  intermediate  in  thickness  between  the  superior  and  the  axillary  borders, 
and  the  portion  of  it  above  the  spine  forms  an  obtuse  angle  with  the  part  below. 
This  border  presents  an  anterior  and  a  posterior  lip,  and  an  intermediate  narrow 
area.  The  anterior  lip  affords  attachment  to  the  Serratus  anterior;  the  posterior 
lip,  to  the  Supraspinatus  above  the  spine,  the   Infraspinatus  below;    the  area 


Fig.  204. — Posterior  view  of  the  thorax  and  shoulder  girdle.     (Morris.) 


between  the  two  lips,  to  the  Levator  scapulae  above  the  triangular  surface  at  the 
commencement  of  the  spine,  to  the  Rhomboideus  minor  on  the  edge  of  that  surface, 
and  to  the  Rhomboideus  major  below  it;  this  last  is  attached  by  means  of  a  fibrous 
arch,  connected  above  to  the  lower  part  of  the  triangular  surface  at  the  base  of 
the  spine,  and  below  to  the  lower  part  of  the  border. 

Angles. — Of  the  three  angles,  the  medial,  formed  by  the  junction  of  the  superior 
and  vertebral  borders,  is  thin,  smooth,  rounded,  inclined  somewhat  lateralward, 
and  gives  attachment  to  a  few  fibers  of  the  Levator  scapulae.  The  inferior  angle, 
thick  and  rough,  is  formed  by  the  union  of  the  vertebral  and  axillary  borders; 
its  dorsal  surface  affords  attachment  to  the  Teres  major  and  frequently  to  a  few 


THE  SCAPULA 


207 


Coracoid 
process 


Acromion 


Infraglenoid  tubercle 


fibers  of  the  Latissimus  dorsi.  The  lateral  angle  is  the  thickest  part  of  the  bone, 
and  is  sometimes  called  the  head  of  the  scapula.  On  it  is  a  shallow  pyriform, 
articular  surface,  the  glenoid  cavity,  which  is  directed  lateralward  and  forward 
and  articulates  with  the  head  of  the  humerus;  it  is  broader  below  than  above 
and  its  vertical  diameter  is  the  longest.  The  surface  is  covered  with  cartilage 
in  the  fresh  state;  and  its  margins,  slightly  raised,  give  attachment  to  a  fibro- 
cartilaginous structure,  the  glenoidal  labrum,  which  deepens  the  cavity.  At  its 
apex  is   a    slight  elevation,  the 

SUpraglenoid    tuberosity,   to    which  Supragleru>id  tubercJe 

the  long  head  of  the  Biceps 
brachii  is  attached.  The  neck 
of  the  scapula  is  the  slightly 
constricted  portion  which  sur- 
rounds the  head;  it  is  more  dis- 
tinct below  and  behind  than 
above  and  in  front. 

The  Coracoid  Process  (processus 
coracoideus) .  —  The  coracoid  pro- 
cess is  a  thick  curved  process  at- 
tached by  a  broad  base  to  the 
u])per  part  of  the  neck  of  the 
scapula;  it  runs  at  first  upward 
and  medialward;  then,  becoming 
smaller,  it  changes  its  direction, 
and  projects  forward  and  lateral- 
ward.  The  ascending  portion, 
flattened  from  before  backward, 
presents  in  front  a  smooth  con- 
cave surface,  across  which  the 
S  ibscapularis  passes.  The  hori- 
zontal portion  is  flattened  from 
al)ove  downward;  its  upper  sur- 
face is  convex  and  irregular,  and 
g  ves  attachment  to  the  Pector- 
ais  minor;  its  under  surface  is 
smooth;  its  medial  and  lateral 
borders  are  rough;  the  former 
g  ves  attachment  to  the  Pectoralis 
n  inor  and  the  latter  to  the  cora- 
coacromial  ligament;  the  apex  is 
embraced  by  the  conjoined  tendon 
o '  origin  of  the  Coracobrachialis 
aid  short  head  of  the  Biceps 
brachii  and  gives  attachment  to 
the  coracoclavicular  fascia.  On 
the  medial  part  of  the  root  of  the 
coracoid  process  is  a  rough  im- 
pression for  the  attachment  of 
the  conoid  ligament;  and  running  from  it  obliquely  forward  and  lateralward, 
on  to  the  upper  surface  of  the  horizontal  portion,  is  an  elevated  ridge  for  the 
ai:tachment  of  the  trapezoid  ligament. 


Fig.  205. 


-Inferior  angle 
-Left  scapula.     Lateral  view. 


I 


Structure.— The  head,  processes,  and  the  thickened  parts  of  the  bone,  contain  cancellous 
ssue;  the  rest  consists  of  a  thin  layer  of  compact  tissue.    The  central  part  of  the  supraspinatous 


208 


OSTEOLOGY 


fossa  and  the  upper  part  of  the  infraspinatous  fossa,  but  especially  the  former,  are  usually  so  thin 
as  to  be  semitransparent;  occasionally  the  bone  is  found  wanting  in  this  situation,  and  the  adjacent 
muscles  are  separated  only  by  fibrous  tissue. 

Ossification  (Fig.  206). — The  scapula  is  ossified  from  seven  or  more  centers:  one  for  the  body, 
two  for  the  coracoid  process,  two  for  the  acromion,  one  for  the  vertebral  border,  and  one  for  the 
inferior  angle. 

Ossification  of  the  body  begins  about  the  second  month  of  fetal  life,  by  the  formation  ol'  an 
irregular  quadrilateral  plate  of  bone,  immediately  behind  the  glenoid  cavity.  This  plate  exte^nds 
so  as  to  form  the  chief  part  of  the  bone,  the  spine  growing  up  from  its  dorsal  surface  about  the 
third  month.  At  birth,  a  large  part  of  the  scapula  is  osseous,  but  the  glenoid  cavity,  the  coraooid 
process,  the  acromion,  the  vertebral  border,  and  the  inferior  angle  are  cartilaginous.  From  the 
fifteenth  to  the  eighteenth  month  after  birth,  ossification  takes  place  in  the  middle  of  the  coraooid 
process,  which  as  a  rule  becomes  joined  with  the  rest  of  the  bone  about  the  fifteenth  year.  Between 
the  fourteenth  and  twentieth  years,  ossification  of  the  remaining  parts  takes  place  in  quick  succes- 
sion, and  usually  in  the  following  order;  first,  in  the  root  of  the  coracoid  process,  in  the  form  of  a 
broad  scale;  secondly,  near  the  base  of  the  acromion;  thirdly,  in  the  inferior  angle  and  contiguous 
part  of  the  vertebral  border;  fourthly,  near  the  extremity  of  the  acromion;  fifthly,  in  the  vertebral 
border.  The  base  of  the  acromion  is  formed  by  an  extension  from  the  spine;  the  two  separate 
nuclei  of  the  acromion  unite,  and  then  join  with  the  extension  from  the  spine.    The  upper  third 


..<^5 


Fia.  206. — Plan  of  ossification  of  the  scapula.     From  seven  centers. 


of  the  glenoid  cavity  is  ossified  from  a  separate  center  (subcoracoid),  which  makes  its  appear- 
ance between  the  tenth  and  eleventh  years  and  joins  between  the  sixteenth  and  the  eighteenth. 
Further,  an  epiphysial  plate  appears  for  the  lower  part  of  the  glenoid  cavity,  while  the  tip  of  the 
coracoid  process  frequently  presents  a  separate  nucleus.  These  various  epiphyses  are  joined 
to  the  bone  by  the  twenty-fifth  year.  Failure  of  bony  union  between  the  acromion  and  spine 
sometimes  occurs,  the  junction  being  effected  by  fibrous  tissue,  or  by  an  imperfect  articulation; 
in  some  cases  of  supposed  fracture  of  the  acromion  with  ligamentous  union,  it  is  probable  that 
the  detached  segment  was  never  united  to  the  rest  of  the  bone. 


THE  HUMERUS  ^^^^^K  209 


The  Humerus  (Arm  Bone). 

The  humerus  (Figs.  207,  208)  is  the  longest  and  largest  bone  of  the  upper 
extremity;  it  is  divisible  into  a  body  and  two  extremities. 

Upper  Extremity. — The  upper  extremity  consists  of  a  large  rounded  head  joined 
to  the  body  by  a  constricted  portion  called  the  neck,  and  two  eminences,  the  greater 
and  lesser  tubercles. 

The  Head  (caput  humeri). — The  head,  nearly  hemispherical  in  form,^  is  directed 
upward,  medialward,  and  a  little  backward,  and  articulates  with  the  glenoid  cavity 
of  the  scapula.  The  circumference  of  its  articular  surface  is  slightly  constricted 
and  is  termed  the  anatomical  neck,  in  contradistinction  to  a  constriction  below  the 
tubercles  called  the  surgical  neck  which  is  frequently  the  seat  of  fracture.  Fracture 
of  the  anatomical  neck  rarely  occurs. 

The  Anatomical  Neck  (collum  anatomicum)  is  obliquely  directed,  forming  an 
obtuse  angle  with  the  body.  It  is  best  marked  in  the  low^er  half  of  its  circum- 
ference; in  the  upper  half  it  is  represented  by  a  narrow  groove  separating  the  head 
from  the  tubercles.  It  affords  attachment  to  the  articular  capsule  of  the  shoulder- 
joint,  and  is  perforated  by  numerous  vascular  foramina. 

The  Greater  Tubercle  (tuberculum  majus;  greater  tuberosity). — The  greater 
tubercle  is  situated  lateral  to  the  head  and  lesser  tubercle.  Its  upper  surface  is 
rounded  and  marked  by  three  flat  impressions :  the  highest  of  these  gives  insertion 
to  the  Supraspinatus;  the  middle  to  the  Infraspinatus;  the  lowest  one,  and  the 
body  of  the  bone  for  about  2.5  cm.  below  it,  to  the  Teres  minor.  The  lateral 
surface  of  the  greater  tubercle  is  convex,  rough,  and  continuous  with  the  lateral 
surface  of  the  body. 

The  Lesser  Tubercle  {tuberculum  minus;  lesser  tuberosity). — The  lesser  tubercle, 
although  smaller,  is  more  prominent  than  the  greater:  it  is  situated  in  front,  and 
hi  directed  medialward  and  forward.  Above  and  in  front  it  presents  an  impression 
for  the  insertion  of  the  tendon  of  the  Subscapularis. 

The  tubercles  are  separated  from  each  other  by  a  deep  groove,  the  intertubercular 
groove  (bicipital  groove),  which  lodges  the  long  tendon  of  the  Biceps  brachii  and 
transmits  a  branch  of  the  anterior  humeral  circumflex  artery  to  the  shoulder-joint. 
It  runs  obliquely  downward,  and  ends  near  the  junction  of  the  upper  with  the 
middle  third  of  the  bone.  In  the  fresh  state  its  upper  part  is  covered  with  a 
thin  layer  of  cartilage,  lined  by  a  prolongation  of  the  synovial  membrane  of  the 
shoulder-joint;  its  lower  portion  gives  insertion  to  the  tendon  of  the  Latissimus 
(lorsi.  It  is  deep  and  narrow  above,  and  becomes  shallow  and  a  little  broader 
J  is  it  descends.  Its  lips  are  called,  respectively,  the  crests  of  the  greater  and  lesser 
tubercles  (bicipital  ridges),  and  form  the  upper  parts  of  the  anterior  and  medial 
borders  of  the  body  of  the  bone. 

The  Body  or  Shaft  (corpus  humeri). — The  body  is  almost  cylindrical  in  the  upper 
lialf  of  its  extent,  prismatic  and  flattened  below,  and  has  three  borders  and  three 
surfaces. 

Borders. — The  anterior  border  runs  from  the  front  of  the  greater  tubercle  above 
t;o  the  coronoid  fossa  below,  separating  the  antero-medial  from  the  antero-lateral 
surface.  Its  upper  partis  a  prominent  ridge,  the  crest  of  the  greater  tubercle; 
it  serves  for  the  insertion  of  the  tendon  of  the  Pectoralis  major.  About  its  center 
it  forms  the  anterior  boundary  of  the  deltoid  tuberosity;  below,  it  is  smooth  and 
rounded,  affording  attachment  to  the  Brachialis. 

The  lateral  border  runs  from  the  back  part  of  the  greater   tubercle  to  the 

'  Though  the  head  is  nearly  hemispherical  in  form,  its  margin,  as  Humphry  has  shown,  is  by  no  means  a  true  circle. 
Its  greatest  diameter  is,  from  the  top  of  the  intertubercular  groove  in  a  direction  downward,  medialward,  and  back- 
ward. Hence  it  follows  that  the  greatest  elevation  of  the  arm  can  be  obtained  by  rolling  the  articular  surface  in  this 
direction — that  is  to  say,  obliquely  upward,  lateralward,  and  forward. 

14 


■ 


210 


OSTEOLOGY 
Articular  capavle 


Surqi4HjU  Neek- 


Brachioradialis 


Common  origin  of" 
Flexor  carpi  radialis 
Palmaris  longua  "'^ 

Flexor  digitorum  svblimis 
Flexor  carpi  vlnaria 


Capit- 
ulum 


-v^ 


Extensor  carpi  radialis 
1  longtis 

,  Articular  capsule 

■  Common  origin  of 

Extensor  carpi  rad.  brev. 
,,    digitorum  convmunia 
,,     digiti  quinti  prop. 
, ,    carpi  idnaris 

Supinator 


Fig.   207. — Left  humerus.     Anterior  view. 


THE  HUMERUS 


1 

I 


I 


lateral  epicondyle,  and  separates  the  antero- 
lateral from  the  posterior  surface.  Its  upper 
half  is  rounded  and  indistinctly  marked,  serv- 
ing for  the  attachment  of  the  lower  part  of  the 
insertion  of  the  Teres  minor,  and  below  this 
giving  origin  to  the  lateral  head  of  the  Triceps 
brachii;  its  center  is  traversed  by  a  broad  but 
shallow  oblique  depression,  the  radial  sulcus 
(musculospiral  groove).  Its  lower  part  forms  a 
prominent,  rough  margin,  a  little  curved  from 
behind  forward,  the  lateral  supracondylar  ridge, 
which  presents  an  anterior  lip  for  the  origin 
of  the  Brachioradialis  above,  and  Extensor 
carpi  radialis  longus  below,  a  posterior  lip  for 
the  Triceps  brachii,  and  an  intermediate  ridge 
for  the  attachment  of  the  lateral  intermuscu- 
lar septum. 

The  medial  border  extends  from  the  lesser 
tubercle  to  the  medial  epicondyle.  Its  upper 
third  consists  of  a  prominent  ridge,  the  crest  of 
the  lesser  tubercle,  which  gives  insertion  to  the 
t(3ndon  of  the  Teres  major.  About  its  center 
is  a  slight  impression  for  the  insertion  of  the 
C!oracobrachialis,  and  just  below  this  is  the 
entrance  of  the  nutrient  canal,  directed  down- 
ward; sometimes  there  is  a  second  nutrient 
canal  at  the  commencement  of  the  radial  sulcus. 
T'he  inferior  third  of  this  border  is  raised  into 
a  slight  ridge,  the  medial  supracondylar  ridge, 
v/hich  becomes  very  prominent  below;  it  pre- 
sents an  anterior  lip  for  the  origins  of  the 
IJrachialis  and  Pronator  teres,  a  posterior  lip 
for  the  medial  head  of  the  Triceps  brachii, 
{.nd  an  intermediate  ridge  for  the  attachment 
of  the  medial  intermuscular  septum. 

Surfaces. — The  antero-lateral  surface  is  di- 
rected lateralward  above,  where  it  is  smooth, 
rounded,  and  covered  by  the  Deltoideus;  for- 
^vard  and  lateralward  below,  where  it  is  slightly 
concave  from  above  downward,  and  gives  origin 
1.0  part  of  the  Brachialis.  About  the  middle 
)f  this  surface  is  a  rough,  triangular  elevation, 
[the  deltoid  tuberosity  for  the  insertion  of  the 
Deltoideus;  below  this  is  the  radial  sulcus, 
directed  obliquely  from  behind,  forward,  and 
downward,  and  transmitting  the  radial  nerve 
and  profunda  artery. 

The  antero-medial  surface,  less  extensive  than 
the  antero-lateral,  is  directed  medialward  above, 
i'orward  and  medialward  below;  its  upper  part 
is  narrow,  and  forms  the  floor  of  the  intertuber- 
cular  groove  which  gives  insertion  to  the  tendon 
of  the  Latissimus  dorsi;  its  middle  part  is 
.slightly  rough  for  the  attachment  of  some  of 


'%.. 


la 

f 

K  (^ 

=^  f 

1     1 

1'^ 

U 

n    f 

H 

1 

a 

>   1 

o    1 

— 

■*    1 

o 

1 

PI 

'^  1 

■0 

§, 

W       J'    M.     1 

1    a       1 

e^  1 

f  »  1 

f  ">  1 

i  "^  1 

■.  <i     1 

>il 

«      I        1 

n 


\ 


Articular 
capsule 


Articular 
capsule 


1  /Vo  cA  i 


Fig.  208. — Left  humerus.     Posterior  view. 


212 


OSTEOLOGY 


the  fibers  of  the  tendon  of  insertion  of  the  Coracobrachialis;  its  loweT  part  is 
smooth,  concave  from  above  downward,  and  gives  origin  to  the  BrachiaHs.^ 

The  posterior  surface  appears  somewhat  twisted,  so  that  its  upper  part  is 
directed  a  Httle  medialward,  its  lower  part  backward  and  a  Httle  laterahvard. 
Nearly  the  whole  of  this  surface  is  covered  by  the  lateral  and  medial  heads  of 
the  Triceps  brachii,  the  former  arising  above,  the  latter  below  the  radial 
sulcus. 

The  Lower  Extremity. — The  lower  extremity  is  flattened  from  before  backward, 
and  curved  slightly  forward;  it  ends  below  in  a  broad,  articular  surface,  which  is 
divided  into  two  parts  by  a  slight  ridge.  Projecting  on  either  side  are  the  latt^ral 
and  medial  epicondyles.  The  articular  sm-face  extends  a  little  lower  than  the 
epicondyles,  and  is  curved  slightly  forward;  its  medial  extremity  occupies  a  lower 
level  than  the  lateral.  The  lateral  portion  of  this  surface  consists  of  a  smooth, 
rounded  eminence,  named  the  capitulum  of  the  humerus;  it  articulates  with  the  cup- 
shaped  depression  on  the  head  of  the  radius,  and  is  limited  to  the  front  and  lower 
part  of  the  bone.  On  the  medial  side  of  this  eminence  is  a  shallow  groove,  in  which 
is  received  the  medial  margin  of  the  head  of  the  radius.  Above  the  front  part 
of  the  capitulum  is  a  slight  depression,  the  radial  fossa,  which  receives  the  anterior 
border  of  the  head  of  the  radius,  when  the  forearm  is  flexed.  The  medial  portion 
of  the  articular  surface  is  named  the  trochlea,  and  presents  a  deep  depression  be- 
tween two  well-marked  borders;  it  is  convex  from  before  backward,  concave  from 
side  to  side,  and  occupies  the  anterior,  lower,  and  posterior  parts  of  the  extremity. 
The  lateral  border  separates  it  from  the  groove  which  articulates  with  the  margin 
of  the  head  of  the  radius.  The  medial  border  is  thicker,  of  greater  length,  and 
consequently  more  prominent,  than  the  lateral.  The  grooved  portion  of  the  artic- 
ular surface  fits  accurately  within  the  semilunar  notch  of  the  ulna;  it  is  broader  and 
deeper  on  the  posterior  than  on  the  anterior  aspect  of  the  bone,  and  is  inclined 
obliquely  downward  and  forward  toward  the  medial  side.  Above  the  front  part 
of  the  trochlea  is  a  small  depression,  the  coronoid  fossa,  which  receives  the  coronoid 
process  of  the  ulna  during  flexion  of  the  forearm.  Above  the  back  part  of  the  troch- 
lea is  a  deep  triangular  depression,  the  olecranon  fossa,  in  which  the  summit  of  the 
olecranon  is  received  in  extension  of  the  forearm.  These  fossae  are  separated  from 
one  another  by  a  thin,  transparent  lamina  of  bone,  which  is  sometimes  perforated 
by  a  supratrochlear  foramen;  they  are  lined  in  the  fresh  state  by  the  synovial 
membrane  of  the  elbow-joint,  and  their  margins  afford  attachment  to  the  anterior 
and  posterior  ligaments  of  this  articulation.  The  lateral  epicondyle  is  a  small, 
tuberculated  eminence,  curved  a  little  forward,  and  giving  attachment  to  the  radial 
collateral  ligament  of  the  elbow-joint,  and  to  a  tendon  common  to  the  origin  of 
the  Supinator  and  some  of  the  Extensor  muscles.  The  medial  epicondyle,  larger 
and  more  prominent  than  the  lateral,  is  directed  a  little  backward;  it  gives  attach- 
ment to  the  ulnar  collateral  ligament  of  the  elbow-joint,  to  the  Pronator  teres, 
and  to  a  common  tendon  of  origin  of  some  of  the  Flexor  muscles  of  the  forearm ; 
the  ulnar  nerve  runs  in  a  groove  on  the  back  of  this  epicondyle.  The  epicondyles 
are  continuous  above  with  the  supracondylar  ridges. 

Structure. — The  extremities  consist  of  cancellous  tissue,  covered  with  a  thin,  compact  layer 
(Fig.  209) ;  the  body  is  composed  of  a  cylinder  of  compact  tissue,  thicker  at  the  center  than  toward 
the  extremities,  and  contains  a  large  medullary  canal  which  extends  along  its  whole  length. 


1  A  small,  hook-shaped  process  of  bone,  the  supracondylar  process,  varying  from  2  to  20  mm.  in  length,  is  not  infre- 
quently found  projectmg  from  the  antero-medial  surface  of  the  body  of  the  humerus  5  cm.  above  the  medial  epicondjle. 
It  is  curved  downward  and  forward,  and  its  pointed  end  is  connected  to  the  medial  border,  just  above  the  medial 
epicondyle,  by  a  fibrous  band,  which  gives  origin  to  a  portion  of  the  Pronator  teres;  through  the  arch  completed  by 
this  fibrous  band  the  median  nerve  and  brachial  artery  pass,  when  these  structures  deviate  from  their  usual  course. 
Sometimes  the  nerve  alone  is  transmitted  through  it,  or  the  nerve  may  be  accompanied  by  the  ulnar  artery,  in  cases 
of  high  division  of  the  brachial.  A  well-marked  groove  is  usually  found  behind  the  process,  in  which  the  nerve  and 
artery  are  lodged.  This  arch  is  the  homologue  of  the  supracondyloid  foramen  found  in  many  animals,  and  probably 
serves  in  them  to  protect  the  nerve  and  artery  from  compression  during  the  contraction  of  the  muscles  in  this  region. 


THE  HUMERUS 


213 


Ossification  (Figs.  210,  211). — The  htimerus  is  ossi- 
fied from  eight  centers,  one  for  each  of  the  following 
parts:  the  body,  the  head,  the  greater  tubercle,  the 
les.ser  tubercle,  the  capitulum,  the  trochlea,  and  one 
for  each  epicondyle.  The  center  for  the  body  appears 
near  the  middle  of  the  bone  in  the  eighth  week  of  fetal 
life,  and  soon  extends  toward  the  extremities.  At  birth 
the  humerus  is  ossified  in  nearly  its  whole  length,  only 
the  extremities  remaining  cartilaginous.  During  the 
first  year,  sometimes  before  birth,  ossification  commences 
in  the  head  of  the  bone,  and  during  the  third  year  the 
center  for  the  greater  tubercle,  and  during  the  fifth  that 
for  the  lesser  tubercle,  make  their  appearance.  By  the 
sixth  year  the  centers  for  the  head  and  tubercles  have 
joined,  so  as  to  form  a  single  large  epiphysis,  which  fuses 
with  the  body  about  the  twentieth  year.  The  lower  end 
of  the  humerus  is  ossified  as  follows.  At  the  end  of 
the  second  year  ossification  begins  in  the  capitulum, 
and  extends  medialward,  to  form  the  chief  part  of  the 
articular  end  of  the  bone;  the  center  for  the  medial  part 
of  the  trochlea  appears  about  the  age  of  twelve.  Ossifi- 
cation begins  in  the  medial  epicondyle  about  the  fifth 
year,  and  in  the  lateral  about  the  thirteenth  or  four- 
teenth year.  About  the  sixteenth  or  seventeenth  year, 
the  lateral  epicondyle  and  both  portions  of  the  articu- 
lating surface,  having  already  joined,  unite  with  the 
body,  and  at  the  eighteenth  year  the  medial  epicon- 
dyle becomes  joined  to  it. 


Epiphysial  line 


Fia.  209. — Longitudinal  section  of  head  of 
left  humerus. 


Epiphyses  of  head  and' 
t  ubercles  blend  at  fifth 
year,  and  unite  with 
body  at  twentieth 
year 


Unites  with  body\  -S 
I  i   at  eighteenth  year  J  ^ 


Bleni  of,  i^t 


Fia.  210. — Plan  of  ossification  of  the  humerus. 


Fig.  211. — Epiphysial  lines  of  humerus  in  a  young 
adult.  Anterior  aspect.  The  lines  of  attachment  of 
the  articular  capsules  are  in  blue. 


JSTEOLOGY 


Olecranons. 


The  Ulna  (Elbow  Bone).i 

The  ulna  (Figs.  212,  213)  is  a  long  bone,  prismatic  in  form,  placed  at  the  maiial 
side  of  the  forearm,  parallel  with  the  radius.  It  is  divisible  into  a  body  and 
two  extremities.  Its  upper  extremity,  of  great  thickness  and  strength,  forms 
a  large  part  of  the  elbow-joint;  the  bone  diminishes  in  size  from  above  downward, 

its  lower  extremity  being  very  small,  and  excluded 
from  the  wrist-joint  by  the  interposition  of  an 
articular  disk. 

The  Upper  Extremity  {proximal  extremity)  (Fig. 
212). — The  upper  extremity  presents  two  curved 
processes,  the  olecranon  and  the  coronoid  process; 
and  two  concave,  articular  cavities,  the  semilunar 
and  radial  notches. 

The  Olecranon  {olecranon  process). — The  olecra- 
non is  a  large,  thick,  curved  eminence,  situated 
at  the  upper  and  back  part  of  the  ulna.  It  is  bent 
forward  at  the  summit  so  as  to  present  a  promi- 
nent lip  which  is  received  into  the  olecranon  fossa 
of  the  humerus  in  extension  of  the  forearm.  Its 
base  is  contracted  where  it  joins  the  body  and  the 
narrowest  part  of  the  upper  end  of  the  ulna.  Its 
posterior  surface,  directed  backward,  is  triangular, 
smooth,  subcutaneous,  and  covered  by  a  bursa. 
Its  superior  surface  is  of  quadrilateral  form,  marked 
behind  by  a  rough  impression  for  the  insertion  of 
the  Triceps  brachii;  and  in  front,  near  the  margin, 
by  a  slight  transverse  groove  for  the  attachment 
of  part  of  the  posterior  ligament  of  the  elbow-joint. 
Its  anterior  surface  is  smooth,  concave,  and  forms 
the  upper  part  of  the  semilunar  notch.  Its  borders 
present  continuations  of  the  groove  on  the  margin 
of  the  superior  surface;  they  serve  for  the  attach- 
ment of  ligaments,  viz.,  the  back  part  of  the  ulnar 
collateral  ligament  medially,  and  the  posterior 
ligament  laterally.  From  the  medial  border  a  part 
of  the  Flexor  carpi  ulnaris  arises;  while  to  the 
lateral  border  the  Anconseus  is  attached. 

The  Coronoid  Process  {processus  coronoideus) . — 
The  coronoid  process  is  a  triangular  eminence 
projecting  forward  from  the  upper  and  front  part 
of  the  ulna.  Its  base  is  continuous  with  the  body 
of  the  bone,  and  of  considerable  strength.  Its 
apex  is  pointed,  slightly  curved  upward,  and  in 
flexion  of  the  forearm  is  received  into  the  coronoid 
fossa  of  the  humerus.  Its  upper  surface  is  smooth,  concave,  and  forms  the  lower 
part  of  the  semilunar  notch.  Its  antero-inferior  surface  is  concave,  and  marked  by 
a  rough  impression  for  the  insertion  of  the  Brachialis.  At  the  junction  of  this 
surface  w  ith  the  front  of  the  body  is  a  rough  eminence,  the  tuberosity  of  the  ulna, 
which  gives  insertion  to  a  part  of  the  Brachialis;  to  the  lateral  border  of  this 
tuberosity  the  oblique  cord  is  attached.  Its  lateral  surface  presents  a  narrow, 
oblong,  articular  depression,  the  radial  notch.    Its  medial  surface,  by  its  prominent, 

1  In  the  anatomical  position,  the  forearm  ia  placed  in  extension  and  supination  with  the  palm  looking  forward 
and  the  thumb  on  the  outer  side. 


Fig.  212. — Upper  extremity  of  left  ulna. 
Lateral  aspect. 


THE  ULNA 


215 


free  margin,  serves  for  the  attachment  of  part  of  the  ulnar  collateral  ligament. 
At  the  front  part  of  this  surface  is  a  small  rounded  eminence  for  the  origin 
of  one  head  of  the  Flexor  digitorum  sublimis;  behind  the  eminence  is  a  depression 
for  part  of  the  origin  of  the  Flexor  digitorum  profundus;  descending  from  the 
eminence  is  a  ridge  which  gives  origin  to  one  head  of  the  Pronator  teres.  Fre- 
quently, the  Flexor  pollicis  longus  arises  from  the  lower  part  of  the  coronoid 
process  by  a  rounded  bundle  of  muscular  fibers. 

The  Semilunar  Notch  {incisura  semilunaris;  greater  sigmoid  cavity). — ^The  semi- 
lunar notch  is  a  large  depression,  formed  by  the  olecranon  and  the  coronoid  process, 
and  serving  for  articulation  with  the  trochlea  of  the  humerus.  About  the  middle 
of  either  side  of  this  notch  is  an  indentation,  which  contracts  it  somewhat,  and 
indicates  the  junction  of  the  olecranon  and  the  coronoid  process.  The  notch  is 
concave  from  above  downward,  and  divided  into  a  medial  and  a  lateral  portion  by 
a  smooth  ridge  running  from  the  summit  of  the  olecranon  to  the  tip  of  the  coronoid 
process.  The  medial  portion  is  the  larger,  and  is  slightly  concave  transversely; 
the  lateral  is  convex  above,  slightly  concave  below. 

The  Radial  Notch  (incisura  radialis;  lesser  sigmoid  cavity). — The  radial  notch 
is  a  narrow,  oblong,  articular  depression  on  the  lateral  side  of  the  coronoid  process ; 
it  receives  the  circumferential  articular  surface  of  the  head  of  the  radius.  It  is 
concave  from  before  backw^ard,  and  its  prominent  extremities  serve  for  the  attach- 
ment of  the  annular  ligament. 

The  Body  or  Shaft  (corpus  ulnce). — The  body  at  its  upper  part  is  prismatic 
in  form,  and  curved  so  as  to  be  convex  behind  and  lateral  ward;  its  central  part 
is  straight;  its  lower  part  is  rounded,  smooth,  and  bent  a  little  lateralward.  It 
tapers  gradually  from  above  downward,  and  has  three  borders  and  three  surfaces. 

Borders. — The  volar  border  (margo  volaris;  anterior  border)  begins  above  at  the 
jDrominent  medial  angle  of  the  coronoid  process,  and  ends  below  in  front  of  the 
styloid  process.  Its  upper  part,  well-defined,  and  its  middle  portion,  smooth  and 
i-ounded,  give  origin  to  the  Flexor  digitorum  profundus;  its  lower  fourth  serves 
'or  the  origin  of  the  Pronator  quadratus.  This  border  separates  the  volar  from 
the  medial  surface. 

The  dorsal  border  (margo  dorsalis;  posterior  border)  begins  above  at  the  apex  of 
I  the  triangular  subcutaneous  surface  at  the  back  part  of  the  olecranon,  and  ends 
below  at  the  back  of  the  styloid  process;  it  is  well-marked  in  the  upper  three- 
fourths,  and  gives  attachment  to  an  aponeurosis  which  affords  a  common  origin  to 
the  Flexor  carpi  ulnaris,  the  Extensor  carpi  ulnaris,  and  the  Flexor  digitorum  pro- 
I  fundus;  its  lower  fourth  is  smooth  and  rounded.  This  border  separates  the  medial 
I  from  the  dorsal  surface. 

The  interosseous  crest  (crista  interossea;  external  or  interosseous  border)  begins 
above  by  the  union  of  two  lines,  which  converge  from  the  extremities  of  the  radial 
notch  and  enclose  between, them  a  triangular  space  for  the  origin  of  part  of  the 
Supinator;  it  ends  below  at  the  head  of  the  ulna.  Its  upper  part  is  sharp,  its  lower 
fourth  smooth  and  rounded.  This  crest  gives  attachment  to  the  interosseous  mem- 
brane, and  separates  the  volar  from  the  dorsal  surface. 

Surf  aces. -^-The  volar  surface  (fades  volaris;  anterior  surface),  much  broader 
I  above  than  below,  is  concave  in  its  upper  three-fourths,  and  gives  origin  to  the 
Flexor  digitorum  profundus;  its  lower  fourth,  also  concave,  is  covered  by  the 
Pronator  quadratus.  The  lower  fourth  is  separated  from  the  remaining  portion 
by  a  ridge,  directed  obliquely  downward  and  medialward,  which  marks  the  extent 
of  origin  of  the  Pronator  quadratus.  At  the  junction  of  the  upper  with  the 
I  middle  third  of  the  bone  is  the  nutrient  canal,  directed  obliquely  upward. 

The  dorsal  surface  (fades  dorsalis;  posterior  surface)  directed  backward  and 
lateralward,  is  broad  and  concave  above;  convex  and  somewhat  narrower  in  the 
I  middle;  narrow,  smooth,  and  rounded  below.    On  its  upper  part  is  an  oblique 


216 


OSTEOLOGY 


Articular  capsule 


Flexor  digilorum 
sublimis 


Prcmator 
teres 


Occasional  origin 
of  Flexor  pollicis  longus 


Articular 
capsule 


Styloid  process 


Radial  origin  of 
Flexor  digitorum 
sublimis 


Brachioradialis 

Groove  for  Abductor 
pollicis  longus  and 
Extensor  pollicis  brevis 


Styloid  process 
Fig.  213. — Bones  of  left  forearm.     Anterior  aspect. 


THE  ULNA 


217 


C Abductor  pollicis 
ForJ  longus 

(Extensor  pollicis 
brevis 


RADIUS 


Articular  capsule 


Flexor  digitorum  sublimit 


Articular  capsule 


For  Ext.  carpi  radialis  longus 
For  Extensor  carpi  radialis  brevia 

For  Extensor  pollicis  longus 

Fia.  214. — Bones  of  left  forearm 


Fen"  Extensor  carpi  vlnaris 
For  Extensor  digiti  quinti  projyrius 


For^ 


Extensor  indicis  proprius 
Extensor  digitorum  communis 

Posterior  aspect. 


218 


OSTEOLOGY 


ridge,  which  runs  from  the  dorsal  end  of  the  radial  notch,  downward  to  the  dorsal 
border;  the  triangular  surface  above  this  ridge  receives  the  insertion  of  the 
Anconseus,  while  the  upper  part  of  the  ridge  affords  attachment  to  the  Supinator. 
Below  this  the  surface  is  subdivided  by  a  longitudinal  ridge,  sometimes  called  the 
perpendicular  line,  into  two  parts:  the  medial  part  is  smooth,  and  covered  by  the 
Extensor  carpi  ulnaris;  the  lateral  portion,  wider  and  rougher,  gives  origin  from 
above  downward  to  the  Supinator,  the  Abductor  pollicis  longus,  the  Extensor  pollicis 
longus,  and  the  Extensor  indicis  proprius. 

The  medial  surface  {fades  medialis;  internal  surface)  is  broad  and  concave 
above,  narrow  and  convex  below.  Its  upper  three-fourths  give  origin  to  the 
Flexor  digitorum  profundus;  its  lower  fourth  is  subcutaneous. 


Olecranon 

Appears  at ,^^^^__  Joins  body  at 

tenth  year      ^^^^     sixteenth  year 


Appears  at  t 
fourth  year 


Joins  body  at 
twentieth  year 


Inferior  extremity 


Fio.  215. — Plan  of  ossification  of  the  ulna. 
From  three'centers. 


FiQ.  216. — Epiphysial  lines  of  ulna  in  a  young  ridult. 
Lateral  aspect.  The  lines  of  attachment  of  the  articular 
capsules  are  in  blue. 


The  Lower  Extremity  {distal  extremity). — The  lower  extremity  of  the  ulna  is 
small,  and  presents  two  eminences;  the  lateral  and  larger  is  a  rounded,  articular 
eminence,  termed  the  head  of  the  ulna;  the  medial,  narrower  and  more  projecting, 
is  a  non-articular  eminence,  the  styloid  process.  The  head  presents  an  articular 
surface,  part  of  which,  of  an  oval  or  semilunar  form,  is  directed  downward,  and 
articulates  with  the  upper  surface  of  the  triangular  articular  disk  which  separates  it 
from  the  wrist-joint;  the  remaining  portion,  directed  lateralward,  is  narrow,  convex, 
and  received  into  the  ulnar  notch  of  the  radius.  The  styloid  process  projects  from 
the  medial  and  back  part  of  the  bone;  it  descends  a  little  lower  than  the  head, 
and  its  rounded  end  affords  attachment  to  the  ulnar  collateral  ligament  of  the 
wrist-joint.  The  head  is  separated  from  the  styloid  process  by  a  depression  for 
the  attachment  of  the  apex  of  the  triangular  articular  disk,  and  behind,  by  a  shallow 
groove  for  the  tendon  of  the  Extensor  carpi  ulnaris. 


THE  RADIUS  WKKKKK         ^^^ 

Structure. — The  long,  narrow  medullary  cavity  is  enclosed  in  a  strong  wall  of  compact  tissue 
which  is  thickest  along  the  interosseous  border  and  dorsal  surface.  At  the  extremities  the  compact 
layer  thins.  The  compact  layer  is  continued  onto  the  back  of  the  olecranon  as  a  plate  of  close 
spongy  bone  with  lamellae  parallel.  From  the  inner  surface  of  this  plate  and  the  compact  layer 
below  it  trabeculae  arch  forward  toward  the  olecranon  and  coronoid  and  cross  other  trabeculse, 
passing  backward  over  the  medullary  cavity  from  the  upper  part  of  the  shaft  below  the  coronoid. 
Below  the  coronoid  process  there  is  a  small  area  of  compact  bone  from  which  trabecule  curve 
ui)ward  to  end  obliquely  to  the  surface  of  the  semilunar  notch  which  is  coated  with  a  thin  layer  of 
compact  bone.     The  trabecular  at  the  lower  end  have  a  more  longitudinal  direction. 

Ossification  (Figs.  215, 216). — The  ulna  is  ossified  from  three  centers:  one  each  for  the  body,  the 
inferior  extremity,  and  the  top  of  the  olecranon.  Ossification  begins  near  the  middle  of  the  body, 
about  the  eighth  week  of  fetal  life,  and  soon  extends  through  the  greater  part  of  the  bone.  At  birth 
the  ends  are  cartilaginous.  About  the  fourth  year,  a  center  appears  in  the  middle  of  the  head, 
and  soon  extends  into  the  styloid  process.  About  the  tenth  year,  a  center  appears  in  the  olecranon 
near  its  extremity,  the  chief  part  of  this  process  being  formed  by  an  upward  extension  of  the  body. 
The  upper  epiphysis  joins  the  body  about  the  sixteenth,  the  lower  about  the  twentieth  year. 

Articulations. — The  ulna  articulates  with  the  humerus  and  radius. 

The  Radius. 

The  radius  (Figs.  213,  214)  is  situated  on  the  lateral  side  of  the  ulna,  which 
exceeds  it  in  length  and  size.  Its  upper  end  is  small,  and  forms  only  a  small  part 
of  the  elbow-joint;  but  its  low^er  end  is  large,  and  forms  the  chief  part  of  the  wrist- 
joint.  It  is  a  long  bone,  prismatic  in  form  and  slightly  curved  longitudinally.  It 
has  a  body  and  two  extremities. 

The  Upper  Extremity  {yroximal  extremity). — The  upper  extremity  presents  a 
head,  neck,  and  tuberosity.  The  head  is  of  a  cylindrical  form,  and  on  its  upper 
surface  is  a  shallow  cup  or  fovea  for  articulation  with  the  capitulum  of  the  humerus. 
The  circumference  of  the  head  is  smooth;  it  is  broad  medially  where  it  articulates 
\Aith  the  radial  notch  of  the  ulna,  narrow  in  the  rest  of  its  extent,  which  is  embraced 
by  the  annular  ligament.  The  head  is  supported  on  a  round,  smooth,  and  con- 
stricted portion  called  the  neck,  on  the  back  of  which  is  a  slight  ridge  for  the  inser- 
tion of  part  of  the  Supinator.  Beneath  the  neck,  on  the  medial  side,  is  an  eminence, 
the  radial  tuberosity;  its  surface  is  divided  into  a  posterior,  rough  portion,  for  the 
i  isertion  of  the  tendon  of  the  Biceps  brachii,  and  an  anterior,  smooth  portion,  on 
v/hich  a  bursa  is  interposed  between  the  tendon  and  the  bone. 

The  Body  or  Shaft  {corpus  radii). — The  body  is  prismoid  in  form,  narrower 
above  than  below,  and  slightly  curved,  so  as  to  be  convex  lateralward.  It  presents 
three  borders  and  three  surfaces. 

Borders. — The  volar  border  {mar go  volaris;  anterior  border)  extends  from  the  lower 
part  of  the  tuberosity  above  to  the  anterior  part  of  the  base  of  the  styloid  process 
below,  and  separates  the  volar  from  the  lateral  surface.  Its  upper  third  is  promi- 
iient,  and  from  its  oblique  direction  has  received  the  name  of  the  oblique  line  of  the 
radius ;  it  gives  origin  to  the  Flexor  digitorum  sublimis  and  Flexor  pollicis  longus ;  the 
surface  above  the  line  gives  insertion  to  part  of  the  Supinator.  The  middle  third  of 
the  volar  border  is  indistinct  and  rounded.  The  lower  fourth  is  prominent,  and  gives 
insertion  to  the  Pronator  quadratus,  and  attachment  to  the  dorsal  carpal  ligament; 
it  ends  in  a  small  tubercle,  into  which  the  tendon  of  the  Brachioradialis  is  inserted. 

The  dorsal  border  {margo  dorsalis;  posterior  border)  begins  above  at  the  back  of 
the  neck,  and  ends  below  at  the  posterior  part  of  the  base  of  the  styloid  process; 
it  separates  the  posterior  from  the  lateral  surface.  It  is  indistinct  above  and  below, 
but  well-marked  in  the  middle  third  of  the  bone. 

The  interosseous  crest  {crista  interossea;  internal  or  interosseous  border)  begins 
above,  at  the  back  part  of  the  tuberosity,  and  its  upper  part  is  rounded  and  indis- 
tinct; it  becomes  sharp  and  prominent  as  it  descends,  and  at  its  lower  part  divides 
into  two  ridges  which  are  continued  to  the  anterior  and  posterior  margins  of  the 
ulnar  notch.    To  the  posterior  of  the  two  ridges  the  lower  part  of  the  interosseous 


OSTEOLOGY 

membrane  is  attached,  while  the  triangular  surface  between  the  ridges  gives  inser- 
tion to  part  of  the  Pronator  quadratus.  This  crest  separates  the  volar  from  the 
dorsal  surface,  and  gives  attachment  to  the  interosseous  membrane. 

Surface. — The  volar  surface  (fades  volaris;  anterior  surface)  is  concave  in  its 
upper  three-fourths,  and  gives  origin  to  the  Flexor  pollicis  longus;  it  is  broad  and  flat 
in  its  lower  fourth,  and  affords  insertion  to  the  Pronator  quadratus.  A  prominent 
ridge  limits  the  insertion  of  the  Pronator  quadratus  below,  and  between  this  and 
the  inferior  border  is  a  triangular  rough  surface  for  the  attachment  of  the  volar 
radiocarpal  ligament.  At  the  junction  of  the  upper  and  middle  thirds  of  the 
volar  surface  is  the  nutrient  foramen,  which  is  directed  obliquely  upward. 

The  dorsal  surface  (fades  dorsalis;  posterior  surface)  is  convex,  and  smooth  in 
the  upper  third  of  its  extent,  and  covered  by  the  Supinator.  Its  middle  third  is 
broad,  slightly  concave,  and  gives  origin  to  the  Abductor  pollicis  longus  above, 
and  the  Extensor  pollicis  brevis  below.  Its  lower  third  is  broad,  convex,  and 
covered  by  the  tendons  of  the  muscles  which  subsequently  run  in  the  grooves  on 
the  lower  end  of  the  bone. 

The  lateral  surface  (fades  lateralis;  external  surface)  is  convex  throughout  its 
entire  extent.  Its  upper  third  gives  insertion  to  the  Supinator.  About  its  center  is 
a  rough  ridge,  for  the  insertion  of  the  Pronator  teres.  Its  lower  part  is  narrow,  and 
covered  by  the  tendons  of  the  Abductor  pollicis  longus  and  Extensor  pollicis  brevis. 

The  Lower  Extremity. — The  lower  extremity  is  large,  of  quadrilateral  form, 
and  provided  with  two  articular  surfaces — one  below,  for  the  carpus,  and  another 
at  the  medial  side,  for  the  ulna.  The  carpal  articular  surface  is  triangular,  concave, 
smooth,  and  divided  by  a  slight  antero-posterior  ridge  into  two  parts.  Of  these, 
the  lateral,  triangular,  articulates  with  the  navicular  bone;  the  medial,  quadri- 
lateral, with  the  lunate  bone.  The  articular  surface  for  the  ulna  is  called  the  ulnar 
notch  (sigmoid  cavity)  of  the  radius;  it  is  narrow,  concave,  smooth,  and  articulates 
with  the  head  of  the  ulna.  These  two  articular  surfaces  are  separated  by  a  promi- 
nent ridge,  to  which  the  base  of  the  triangular  articular  disk  is  attached ;  this  disk 
separates  the  wrist-joint  from  the  distal  radioulnar  articulation.  This  end  of  the 
bone  has  three  non-articular  surfaces — volar,  dorsal,  and  lateral.  The  volar  surface, 
rough  and  irregular,  affords  attachment  to  the  volar  radiocarpal  ligament.  The 
dorsal  surface  is  convex,  affords  attachment  to  the  dorsal  radiocarpal  ligament, 
and  is  marked  by  three  grooves.  Enumerated  from  the  lateral  side,  the  first 
groove  is  broad,  but  shallow,  and  subdivided  into  two  by  a  slight  ridge;  the  lateral 
of  these  two  transmits  the  tendon  of  the  Extensor  carpi  radialis  longus,  the  medial 
the  tendon  of  the  Extensor  carpi  radialis  brevis.  The  second  is  deep  but  narrow, 
and  bounded  laterally  by  a  sharply  defined  ridge ;  it  is  directed  obliquely  from  above 
downward  and  lateralward,  and  transmits  the  tendon  of  the  Extensor  pollicis 
longus.  The  third  is  broad,  for  the  passage  of  the  tendons  of  the  Extensor  indicis 
proprius  and  Extensor  digitorum  communis.  The  lateral  surface  is  prolonged 
obliquely  downward  into  a  strong,  conical  projection,  the  styloid  process,  which 
gives  attachment  by  its  base  to  the  tendon  of  the  Brachioradialis,  and  by  its  apex 
to  the  radial  collateral  ligament  of  the  wrist-joint.  The  lateral  surface  of  this 
process  is  marked  by  a  flat  groove,  for  the  tendons  of  the  Abductor  pollicis  longus 
and  Extensor  pollicis  brevis. 

Structure. — The  long  narrow  medullary  cavity  is  enclosed  in  a  strong  wall  of  compact  tissue 
which  is  thickest  along  the  interosseous  border  and  thinnest  at  the  extremities  except  over  the 
cup-shaped  articular  surface  (fovea)  of  the  head  where  it  is  thickened.  The  trabecular  of  the 
spongy  tissue  are  somewhat  arched  at  the  upper  end  and  pass  upward  from  the  compact  layer  of 
the  shaft  to  the  fovea  capituli;  they  are  crossed  by  others  parallel  to  the  surface  of  the  fovea. 
The  arrangement  at  the  lower  end  is  somewhat  similar. 

Ossification  (Figs.  217,  218). — The  radius  is  ossified  from  three  centers:  one  for  the  body, 
and  one  for  either  extremity.  That  for  the  body  makes  its  appearance  near  the  center  of  the  bone, 
during  the  eighth  week  of  fetal  hfe.    About  the  end  of  the  second  year,  ossification  commences 


THE  CARPUS 

in  the  lower  end;  and  at  the  fifth  year,  in  the  upper  end.  The  upper  epiphysis  fuses  with  the 
body  at  the  age  of  seventeen  or  eighteen  years,  the  lower  about  the  age  of  twenty.  An  additional 
center  sometimes  found  in  the  radial  tuberosity,  appears  about  the  fourteenth  or  fifteenth  year. 


Herid 


Appears  at 
fifth  year 


Unites  with  body 
about  pvherty 


Unites  with  body 
about  ttoentieth 
year 


Lower  extremity 


Fig.  217.- 


-Plan  of  ossification  of  the  radius. 
From  three  centers. 


Fig.  218. — Epiphysial  lines  of  radius  in  a  young 
adult.  Anterior  aspect.  The  line  of  attachment  of  the 
articular  capsule  of  the  wrist-joint  is  in  blue. 


THE  HAND. 


I 

^H    The  skeleton  of  the  hand  (Figs.  219,  220)  is  subdivided  into  three  segments:  the 
^■carpus  or  wrist  bones;  the  metacarpus  or  bones  of  the  palm;  and  the  phalanges  or 
^■bones  of  the  digits. 
^M  The  Carpus  (Ossa  Carpi). 

^H    The  carpal  bones,  eight  in  number,  are  arranged  in  two  rows.    Those  of  the 
^■|)roximal  row,  from  the  radial  to  the  ulnar  side,  are  named  the  navicular,  lunate, 
^^triangular,  and  pisiform ;  those  of  the  distal  row,  in  the  same  order,  are  named  the 
greater  multangular,  lesser  multangular,  capitate,  and  hamate. 

Common  Characteristics  of  the  Carpal  Bones. — Each  bone  (excepting  the  pisi- 
form) presents  six  surfaces.  Of  these  the  volar  or  anterior  and  the  dorsal  or  posterior 
surfaces  are  rough,  for  ligamentous  attachment;  the  dorsal  surfaces  being  the 
broader,  except  in  the  navicular  and  lunate.  The  s^ijjerior  or  proximal,  and  inferior 
or  distal  surfaces  are  articular,  the  superior  generally  convex,  the  inferior  concave; 
the  medial  and  lateral  surfaces  are  also  articular  where  they  are  in  contact  with 
contiguous  bones,  otherwise  they  are  rough  and  tuberculated.  The  structure  in 
all  is  similar,  viz.,  cancellous  tissue  enclosed  in  a  layer  of  compact  bone. 

Bones  of  the  Proximal  Row  {upper  row). — The  Navicular  Bone  (os  naviculare  manus; 
scaphoid  bone)  (Fig.  221), — The  navicular  bone  is  the  largest  bone  of  the  proximal 
row,  and  has  received  its  name  from  its  fancied  resemblance  to  a  boat.  It  is  situated 
at  the  radial  side  of  the  carpus,  its  long  axis  being  from  above  downward,  lateralward, 
and  forward.    The  superior  surface  is  convex,  smooth,  of  triangular  shape,  and  artic- 


222 


OSTEOLOGY 


ulates  with  the  lower  end  of  the  radius.  The  inferior  surface,  directed  downwaiv 
lateralward,  and  backward,  is  also  smooth,  convex,  and  triangular,  and  is  divided 
by  a  slight  ridge  into  two  parts,  the  lateral  articulating  with  the  greater  multangu- 
lar, the  medial  with  the  lesser  multangillar.  On  the  dorsal  surface  is  a  narrow, 
rough  groove,  which  runs  the  entire  length  of  the  bone,  and  serves  for  the  attach- 
ment of  ligaments.  The  volar  surface  is  concave  above,  and  elevated  at  its  lower 
and  lateral  part  into  a  rounded  projection,  the  tubercle,  which  is  directed  forward 


Carpus 

Flexor  carpi  ulnakis 
Flexor  digiti  quinti  bkevis 

OpPONENS  I>IQITI  QUINTl 


Metacarpus 


Groove  for  tendon  of 
Flexor  carpi  radialis 

Opponens  pollicis 
Flexor  polucis  brkvis 


//Abductor  pollicis 


Flexor  brevis'\ 

AND  I 

Abductor      J    "' 

digiti  QniNTI.    / 


Sesamoid 

bones 


Abductor 
pollicis 
brevis 


Flexor  digitorum  sublimis 


Flexor  digitorum  profundus 


FiQ.  219. — Bones  of  the  left  hand.     Volar  surface. 


I 


THE  CARPUS 


223 


and  gives  attachment  to  the  transverse  carpal  ligament  and  sometimes  origin  to 
a  few  fibers  of  the  Abductor  pollicis  brevis.  The  lateral  surface  is  rough  and  narrow, 
and  gives  attachment  to  the  radial  collateral  ligament  of  the  wrist.  The  medial 
surface  presents  two  articular  facets;  of  these,  the  superior  or  smaller  is  flattened 
of  semilunar  form,  and  articulates  with  the  lunate  bone;  the  inferior  or  larger  is 
concave,  forming  with  the  lunate  a  concavity  for  the  head  of  the  capitate  bone. 


CARPI  RADIALIS 
LONG0S 

BXT.  CARPI  RADIALIS 
BREVIS 


sr-fjiffw 


Fig.  220. — Boaes  of  the  left  hand.     Dorsal  surface. 


224 


OSTEOLOGY 


Articulations. — The  navicular  articulates  with  five  bones:  the  radius  proximally,  greater  and 
lesser  multangulars  distally,  and  capitate  and  lunate  medially. 

The  Lunate  Bone  (os  lunatum;  semilunar  bone)  (Fig.  222). — The  lunate  bone  may 
be  distinguished  by  its  deep  concavity  and  crescentic  outHne.  It  is  situated  in 
the  center  of  the  proximal  row  of  the  carpus,  between  the  navicular  and  triangul  ar. 
The  superior  surface,  convex  and  smooth,  articulates  with  the  radius.  The  inferior 
surface  is  deeply  concave,  and  of  greater  extent  from  before  backward  than  trans- 


For  radius 


For  lunate 


Tubercle 

\ 


For  greater 
multangular 


For  capitate 


For  lesser  multangular 
Fig.  221. — The  left  navicular  bone. 


versely:  it  articulates  with  the  head  of  the  capitate,  and,  by  a  long,  narrow  facet 
(separated  by  a  ridge  from  the  general  surface),  with  the  hamate.  The  dorsal 
and  volar  surfaces  are  rough,  for  the  attachment  of  ligaments,  the  former  being 
the  broader,  and  of  a  somewhat  rounded  form.     The  lateral  surface  presents  a 


For  triangular 


For  radius 


For  navicular 
For  Iiamate      For  capitate 

Fig.  222.— The  left  lunate  bone. 

narrow,  flattened,  semilunar  facet  for  articulation  with  the  navicular.  The  medial 
surface  is  marked  by  a  smooth,  quadrilateral  facet,  for  articulation  with  the 
triangular. 

Articulations. — The  lunate  articulates  with  five  bones:     the  radius  proximally,  capitate  and 
hamate  distally,  navicular  laterally,  and  triangular  medially. 


For  pisiform 


For  lunate 


For  triangular 


For  hamate 
Fig.  223.— The  left  triangular  bone. 


Fig.  224. — The  left  pisiform  bone. 


The  Triangular  Bone  (os  triquetum;  cuneiform  hone)  (Fig.  223). — The  triangular 
bone  may  be  distinguished  by  its  pyramidal  shape,  and  by  an  oval  isolated  facet 
for  articulation  with  the  pisiform  bone.  It  is  situated  at  the  upper  and  ulnar  side 
of  the  carpus.  The  superior  surface  presents  a  medial,  rough,  non-articular  portion, 
and  a  lateral  convex  articular  portion  which  articulates  with  the  triangular  articular 
disk  of  the  wrist.  The  inferior  surface,  directed  lateralward,  is  concave,  sinuously 
curved,  and  smooth  for  articulation  with  the  hamate.  The  dorsal  surface  is  rough 
for  the  attachment  of  ligaments.    The  volar  surface  presents,  on  its  medial  part, 


THE  CARPUS 


225 


an  oval  facet,  for  articulation  with  the  pisiform;  its  lateral  part  is  rough  for  liga- 
mentous attacliment.  The  lateral  surface,  the  base  of  the  pyramid,  is  marked  by  a 
fiat,  quadrilateral  facet,  for  articulation  with  the  lunate.  The  medial  surface, 
the  summit  of  the  pyramid,  is  pointed  and  roughened,  for  the  attachment  of  the 
» ulnar  collateral  ligament  of  the  wrist. 

Ar^'culations. — The  triangular  articulates  with  three  bones:  the  lunate  laterally,  the  pisiform 
in  front,  the  hamate  distaUy;  and  with  the  triangular  articular  disk  which  separates  it  from  the 
lower  end  of  the  ulna. 

The  Pisiform  Bone  (os  pisiforme)  (Fig.  224). — The  pisiform  bone  may  be  known 
by  its  small  size,  and  by  its  presenting  a  single  articular  facet.  It  is  situated  on  a 
plane  anterior  to  the  other  carpal  bones  and  is  spheroidal  in  form.  Its  dorsal 
surface  presents  a  smooth,  oval  facet,  for  articulation  with  the  triangular :  this  facet 
approaches  the  superior,  but  not  the  inferior  border  of  the  bone.  The  volar  surface 
is  rounded  and  rough,  and  gives  attachment  to  the  transverse  carpal  ligament, 
and  to  the  Flexor  carpi  ulnaris  and  Abductor  digiti  quinti.  The  lateral  and  medial 
surfaces  are  also  rough,  the  former  being  concave,  the  latter  usually  convex. 

Articulation. — The  pisiform  articulates  with  one  bone,  the  triangular. 

Bones  of  the  Distal  Row  {lower  row). — The  Greater  Multangular  Bone  (os  mul- 
tangulum  majus;  trapezium)  (Fig.  225). — The  greater  multangular  bone  may  be 
distinguished  by  a  deep  groove  on  its  volar  surface.  It  is  situated  at  the  radial 
side  of  the  carpus,  between  the  navicular  and  the  first  metacarpal  bone.  The 
superior  surface  is  directed  upward  and  medialward;  medially  it  is  smooth,  and 
articulates  with  the  navicular ;  laterally  it  is  rough  and  continuous  with  the  lateral 
surface.  The  inferior  surface  is  oval,  concave  from  side  to  side,  convex  from  before 
backward,  so  as  to  form  a  saddle-shaped  surface  for  articulation  with  the  base 


For  lesser 
vivitangtdar 


Groove 


For  navicular 


For  2nd 
metacarpal 


Ridge 


For  \st  metacarpal 

Fig.  225. — The  left  greater  multangular  bone 


For  lesser 
mvltanguMT 


For  2)id  metacarpal 


)f  the  first  metacarpal  bone.  The  dorsal  surface  is  rough.  The  volar  surface  is 
barrow  and  rough.  At  its  upper  part  is  a  deep  groove,  running  from  above  obliquely 
pownward  and  medialward;  it  transmits  the  tendon  of  the  Flexor  carpi  radialis, 
^nd  is  bounded  laterally  by  an  oblique  ridge.  This  surface  gives  origin  to  the 
Opponens  pollicis  and  to  the  Abductor  and  Flexor  pollicis  brevis;  it  also  affords 
attachment  to  the  transverse  carpal  ligament.  The  lateral  surface  is  broad  and 
rough,  for  the  attachment  of  ligaments.  The  medial  surface  presents  two  facets; 
the  upper,  large  and  concave,  articulates  with  the  lesser  multangular;  the  lower, 
small  and  oval,  with  the  base  of  the  second  metacarpal. 

;    Articulations. — The  greater  multangular  articulates  with  four  bones :    the  navicular  proximally, 
[  the  first  metacarpal  distally,  and  the  lesser  multangular  and  second  metacarpal  medially. 

The  Lesser  Multangular  Bone  (os  multangulum  minus;  trapezoid  hone)  (Fig.  226). 
-The  lesser  multangular  is  the  smallest  bone  in  the  distal  row.    It  may  be  known 
llby  its  wedge-shaped  form,  the  broad  end   of  the  wedge  constituting  the  dorsal, 
l^he  narrow  end  the  volar  surface;  and  by  its  having  four  articular  facets  touching 
ich  other,  and  separated  by  sharp  edges.     The  superior  surface,  quadrilateral, 
15 


226 


OSTEOLOGY 


For  navicular 


Volar 
surface 


For  greater 
multangular 


smooth,  and  slightly  concave,  articulates  with  the  navicular.  The  inferioT'surFace 
articulates  with  the  proximal  end  of  the  second  metacarpal  bone;  it  is  convex  from 
side  to  side,  concave  from  before  backward  and  subdivided  by  an  elevated  ridge  into 

two  unequal  facets.  The  dorsal  and  volar 
surfaces  are  rough  for  the  attachment  of 
ligaments,  the  former  being  the  larger 
of  the  two.  The  lateral  surface,  con\'ex 
and  smooth,  articulates  with  the  greater 
multangular.  The  medial  surface  is  con- 
cave and  smooth  in  front,  for  artic- 
ulation with  the  capitate;  rough  behind, 
for  the  attachment  of  an  interosseous 
ligament. 


For 

capitate 


Dorsal 

surface 

Fig.  226. — The  left  lesser  multangular  bone. 


For  2nd 

vielacarpal 


Articulations. — The  lesser  multangular  articulates  with /our  bones:  the  navicular  proximally, 
second  metacarpal  distally,  greater  multangular  laterally,  and  capitate  medially. 

The  Capitate  Bone  {os  capitatum;  os  magnum)  (Fig.  227). — The  capitate  bone 
is  the  largest  of  the  carpal  bones,  and  occupies  the  center  of  the  wrist.  It  presents, 
above,  a  rounded  portion  or  head,  which  is  received  into  the  concavity  formed  by 


For  lunate 


For 

navicular 


For  lesser 
multangular 


For 
hamate 


For  3rd 

For  2nd     metacarpal 
metacarpal 


For  4ih  metacarpal 
Fig.   227.— The  left  capitate  bone. 


Volar  surface 


the  navicular  and  lunate;  a  constricted  portion  or  neck;  and  below  this,  the  body. 
The  superior  surface  is  round,  smooth,  and  articulates  with  the  lunate.  The  inferior 
surface  is  divided  by  two  ridges  into  three  facets,  for  articulation  with  the  second, 
third,  and  fourth  metacarpal  bones,  that  for  the  third  being  the  largest.  The 
dorsal  surface  is  broad  and  rough.  The  volar  surface  is  narrow,  rounded,  and  rough, 
for  the  attachment  of  ligaments  and  a  part  of  the  Adductor  pollicis  obliquus. 


For  lunate 


For  triangular 


For  capitate 
For  Ath  metacarpal 


For  5th  metacarpal 


Hamulus 

Fig.   228.— The  left  hamate  bone. 


For  5th  metacarpal 


The  lateral  surface  articulates  with  the  lesser  multangular  by  a  small  facet  at 
its  anterior  inferior  angle,  behind  which  is  a  rough  depression  for  the  attach- 
ment of  an  interosseous  ligament.  Above  this  is  a  deep,  rough  groove,  forming 
part  of  the  neck,  and  serving  for  the  attachment  of  ligaments;  it  is  bounded  supe- 
riorly by  a  smooth,  convex  surface,  for  articulation  with  the  navicular.    The  medial 


I 


THE  METACARPUS 


I 


surface  articulates  with  the  hamate  by  a  smooth,  concave,  oblong  facet,  which 
occupies  its  posterior  and  superior  parts;  it  is  rough  in  front,  for  the  attachment 
of  an  interosseous  ligament. 

Articulations. — The  capitate  articulates  with  seven  bones :  the  navicular  and  lunate  proximally, 
the  second,  third,  and  fourth  metacarpals  distally,  the  lesser  multangular  on  the  radial  side,  and 
the  hamate  on  the  ulnar  side. 

The  Hamate  Bone  {os  hamaium;  unciform  bone)  (Fig.  228). — The  hamate  bone 
may  be  readily  distinguished  by  its  wedge-shaped  form,  and  the  hook-like  process 
which  projects  from  its  volar  surface.  It  is  situated  at  the  medial  and  lower  angle 
of  the  carpus,  with  its  base  downward,  resting  on  the  fourth  and  fifth  metacarpal 
bones,  and  its  apex  directed  upward  and  lateralward.  The  superior  surface,  the 
ai)ex  of  the  wedge,  is  narrow,  convex,  smooth,  and  articulates  with  the  lunate. 
The  inferior  surface  articulates  with  the  fourth  and  fifth  metacarpal  bones,  by 
concave  facets  which  are  separated  by  a  ridge.  The  dorsal  surface  is  triangular 
and  rough  for  ligamentous  attachment.  The  volar  surface  presents,  at  its  lower 
and  ulnar  side,  a  curved,  hook-like  process,  the  hamulus,  directed  forward  and 
lateralward.  This  process  gives  attachment,  by  its  apex,  to  the  transverse  carpal 
ligament  and  the  Flexor  carpi  ulnaris;  by  its  medial  surface  to  the  Flexor  brevis 
and  Opponens  digiti  quinti;  its  lateral  side  is  grooved  for  the  passage  of  the  Flexor 
tendons  into  the  palm  of  the  hand.  It  is  one  of  the  four  eminences  on  the  front 
of  the  carpus  to  which  the  transverse  carpal  ligament  of  the  wrist  is  attached; 
tlie  others  being  the  pisiform  medially,  the  oblique  ridge  of  the  greater  multangular 
and  the  tubercle  of  the  navicular  laterally.  The  medial  surface  articulates  with 
tlie  triangular  bone  by  an  oblong  facet,  cut  obliquely  from  above,  downward 
and  medial  ward.  The  lateral  surface  articulates  with  the  capitate  by  its  upper 
and  posterior  part,  the  remaining  portion  being  rough,  for  the  attachment  of 
ligaments. 

Articulations. — The  hamate  articulates  with  five  bones:     the  lunate  proximally,  the  fourth 
fth  metacarpals  distally,  the  triangular  medially,  the  capitate  laterally. 


^f 


The  Metacarpus. 


I 


The  metacarpus  consists  of  five  cylindrical  bones  which  are  numbered  from  the 
iteral  side  {ossa  metacarpalia  I-V) ;  each  consists  of  a  body  and  two  extremities. 

Common  Characteristics  of  the  Metacarpal  Bones.— The  Body  (corpus;  shaft). — 
?he  body  is  prismoid  in  form,  and  curved,  so  as  to  be  convex  in  the  longitudinal 
lirection  behind,  concave  in  front.  It  presents  three  surfaces:  medial,  lateral, 
iid  dorsal.  The  medial  and  lateral  surfaces  are  concave,  for  the  attachment  of 
he  Interossei,  and  separated  from  one  another  by  a  prominent  anterior  ridge. 

^[Tie  dorsal  surface  presents  in  its  distal  two-thirds  a  smooth,  triangular,  flattened 
jea  which  is  covered  in  the  fresh  state,  by  the  tendons  of  the  Extensor  muscles. 
This  surface  is  bounded  by  two  lines,  which  commence  in  small  tubercles  situated 
>n  either  side  of  the  digital  extremity,  and,  passing  upward,  converge  and  meet 
bme  distance  above  the  center  of  the  bone  and  form  a  ridge  which  runs  along  the 
test  of  the  dorsal  surface  to  the  carpal  extremity.  This  ridge  separates  two 
'oping  surfaces  for  the  attachment  of  the  Interossei  dorsales.  To  the  tubercles 
»n  the  digital  extremities  are  attached  the  collateral  ligaments  of  the  metacarpo- 
phalangeal joints. 

The  Base  or  Carpal  Extremity  (basis)  is  of  a  cuboidal  form,  and  broader  behind 
lian  in  front:  it  articulates  with  the  carpus,  and  with  the  adjoining  metacarpal 
>ones;  its  dorsal  and  volar  surfaces  are  rough,  for  the  attachment  of  ligaments. 
[  The  Head  or  Digital  Extremity  (capitulum)  presents  an  oblong  surface  markedly 

'convex  from  before  backward,  less  so  transversely,  and  flattened  from  side  to  side; 

it  articulates  with  the  proximal  phalanx.    It  is  broader,  and  extends  farther  up- 


228 


For  greater 
multangular 


For  greater 
multangular 


FiQ.  229. — The  first  metacarpal. 
(Left.) 


ward,  on  the  volar  than  on  the  dorsal  aspect,  and  is  longer  in  the  antero-post(;rior 
than  in  the  transverse  diameter.  On  either  side  of  the  head  is  a  tubercle  for  the 
attachment  of  the  collateral  ligament  of  the  metacarpophalangeal  joint.  The 
dorsal  surface,  broad  and  flat,  supports  the  Extensor  tendons;  the  volar  smface 
is  grooved  in  the  middle  line  for  the  passage  of  the  Flexor  tendons,  and  mai-ked 
on  either  side  by  an  articular  eminence  continuous  with  the  terminal  articular 
surface. 

Characteristics  of  the  Individual  Metacarpal  Bones. — The  First  Metacarpal 
Bone  {os  vietacarpale  I;  metacarpal  bone  of  the  thumb)  (Fig.  229)  is  shorter  and 

stouter  than  the  others,  diverges  to  a  greater  degree 
from  the  carpus,  and  its  volar  surface  is  directed 
toward  the  palm.  The  body  is  flattened  and  broad 
on  its  dorsal  surface,  and  does  not  present  the  ridge 
which  is  found  on  the  other  metacarpal  bones;  its 
volar  surface  is  concave  from  above  downward.  On 
its  radial  border  is  inserted  the  Opponens  pollicis; 
its  ulnar  border  gives  origin  to  the  lateral  head  of 
the  first  Interosseus  dorsalis.  The  base  presents  a 
concavo-convex  surface,  for  articulation  with  the 
greater  multangular;  it  has  no  facets  on  its  sides,  but 
on  its  radial  side  is  a  tubercle  for  the  insertion  of  the 
Abductor  pollicis  longus.  The  head  is  less  convex 
than  those  of  the  other  metacarpal  bones,  and  is 
broader  from  side  to  side  than  from  before  backward. 
On  its  volar  surface  are  two  articular  eminences,  of 
which  the  lateral  is  the  larger,  for  the  two  sesamoid 
bones  in  the  tendons  of  the  Flexor  pollicis  brevis. 
The  Second  Metacarpal  Bone  (os  metacarpale  II;  metacarpal  bone  of  the  index 
finger)  (Fig.  230)  is  the  longest,  and  its  base  the  largest,  of  the  four  remaining 
bones.  Its  base  is  prolonged  upward  and  medialward,  forming  a  prominent  ridge. 
It  presents  four  articular  facets:  three  on  the  upper  surface  and  one  on  the  ulnar 
side.  Of  the  facets  on  the  upper  surface  the  intermediate  is  the  largest  and  is 
concave  from  side  to  side,  convex  from  before  backward  for  articulation  with  the 
lesser  multangular;  the  lateral  is  small,  flat  and  oval  for  articulation  with  the  greater 
multangular;  the  medial,  on  the  summit  of  the  ridge,  is  long  and  narrow  for  articu- 
lation with  the  capitate.  The  facet  on  the  ulnar  side  articulates  with  the  third 
metacarpal.  The  Extensor  carpi  radialis  longus  is  inserted  on  the  dorsal  surface 
and  the  Flexor  carpi  radialis  on  the  volar  surface  of  the  base. 

The  Third  Metacarpal  Bone  {os  metacarpale  III;  metacarpal  bone  of  the  middle 
finger)  (Fig.  231)  is  a  little  smaller  than  the  second.  The  dorsal  aspect  of  its 
base  presents  on  its  radial  side  a  pyramidal  eminence,  the  styloid  process,  which 
extends  upward  behind  the  capitate;  immediately  distal  to  this  is  a  rough  surface 
for  the  attachment  of  the  Extensor  carpi  radialis  brevis.  The  carpal  articular 
facet  is  concave  behind,  flat  in  front,  and  articulates  with  the  capitate.  On  the 
radial  side  is  a  smooth,  concave  facet  for  articulation  with  the  second  metacarpal, 
and  on  the  ulnar  side  two  small  oval  facets  for  the  fourth  metacarpal. 

The  Fourth  Metacarpal  Bone  {os  metacarpale  IV;  metacarpal  bone  of  the  ring 
finger)  (Fig.  232)  is  shorter  and  smaller  than  the  third.  The  base  is  small  and 
quadrilateral;  its  superior  surface  presents  two  facets,  a  large  one  medially  for 
articulation  with  the  hamate,  and  a  small  one  laterally  for  the  capitate.  On  the 
radial  side  are  two  oval  facets,  for  articulation  with  the  third  metacarpal ;  and  on 
the  ulnar  side  a  single  concave  facet,  for  the  fifth  metacarpal. 

The  Fifth  Metacarpal  Bone  {os  metacarpale  V;  metacarpal  bone  of  the  little  finger) 
(Fig.  233)  presents  on  its  base  one  facet  on  its  superior  surface,  which  is  concavo- 


THE  METACARPUS 


229 


convex  and  articulates  with  the  hamate,  and  one  on  its  radial  side,  which  articulates 
with  the  fourth  metacarpal.  On  its  ulnar  side  is  a  prominent  tubercle  for  the  inser- 
tion of  the  tendon  of  the  Extensor  carpi  ulnaris.    The  dorsal  surface  of  the  body 


For  greater         For  '6rd 
Fo  '•  lesser    multangxdar    metacarpal      For      For  lesser 
mt  Uangular  capitate     mult- 

angular 

Fio.  230. — The  second  metacarpal.     (Left.) 


Styloid  Far  2nd 
process     meta- 
carpal 

Fig.  231. — The  third  metacarpal.     (Left.) 


For 
capitate 


For  ^th 
metacarpal 


is  divided  by  an  oblique  ridge,  which  extends  from  near  the  ulnar  side  of  the  base 
to  the  radial  side  of  the  head.  The  lateral  part  of  this  surface  serves  for  the  attach- 
mjnt  of  the  fourth  Interosseus  dorsalis;  the  medial  part  is  smooth,  triangular,  and 
covered  by  the  Extensor  tendons  of  the  little  finger. 

•f 


For 
capitate 


For  3rd 


For 


For  5th 

metO' 
carpal 


metacarpal    hamate 
Fig.  232.— The  fourth  metacarpal.     (Left.) 


For  4:th 
metacarpal 


For  hamate 


Fig.  233. — The  fifth  metacarpal.     (Left.) 


Articulations. — Besides  their  phalangeal  articulations,  the  metacarpal  bones  articulate  as 
follows:  the  first  with  the  greater  multangular;  the  second  with  the  greater  multangular,  lesser 
multangular,  capitate  and  third  metacarpal;  the  third  with  the  capitate  and  second  and  fourth 
metacarpals;  the  fourth  with  the  capitate,  hamate,  and  third  and  fifth  metacarpals;  and  the 
fifth  with  the  hamate  and  fourth  metacarpal. 


230 


OSTEOLOGY 


The  Phalanges  of  the  Hand  (Phalanges  Digitonim  Manus). 

The  phalanges  are  fourteen  in  number,  three  for  each  finger,  and  two  for  the 
thumb.  Each  consists  of  a  body  and  two  extremities.  The  body  tapers  from  above 
downward,  is  convex  posteriorly,  concave  in  front  from  above  downward,  flat 
from  side  to  side;  its  sides  are  marked  by  rough  ridges  which  give  attachment 
to  the  fibrous  sheaths  of  the  Flexor  tendons.  The  proximal  extremities  of  the  bones 
of  the  first  row  present  oval,  concave  articular  surfaces,  broader  from  side  to  side 
than  from  before  backward.  The  proximal  extremity  of  each  of  the  bones  of  the 
second  and  third  rows  presents  a  double  concavity  separated  by  a  median  ridge. 
The  distal  extremities  are  smaller  than  the  proximal,  and  each  ends  in  two  condyles 
separated  by  a  shallow  groove;  the  articular  surface  extends  farther  on  the  volar 
than  on  the  dorsal  surface,  a  condition  best  marked  in  the  bones  of  the  first  row. 

The  ungual  phalanges  are  convex  on  their  dorsal  and  flat  on  their  volar  surfaces; 
they  are  recognized  by  their  small  size,  and  by  a  roughened,  elevated  surface  of 
a  horseshoe  form  on  the  volar  surface  of  the  distal  extremity  of  each  which  serves 
to  support  the  sensitive  pulp  of  the  finger. 


One  center  for  each  hone  : 
All  cartilaginous  at  birth 


METACARPALS  OF  FINGERS 

Tloo  centers  for  each  bone  . 
One  for  body 
One  for  head 


PHALANOZIS 

Two  centers  for  each  bone 
One  for  body 
One  for  proximal 
extremity 


ajifieari  /^-S*r  y  t- 
\    unite  18  ZO'^yZ. 


FiG.   234. — Plan  of  ossification  of  the  hand. 

Articulations. — In  the  four  fingers  the  phalanges  of  the  first  row  articulate  with  those  of  the 
second  row  and  with  the  metacarpals;  the  phalanges  of  the  second  row  with  those  of  the  first 
and  third  rows,  and  the  ungual  phalanges  with  those  of  the  second  row.  In  the  thumb,  which 
has  only  two  phalanges,  the  first  phalanx  articulates  by  its  proximal  extremity  with  the  meta- 
carpal bone  and  by  its  distal  with  the  ungual  phalanx. 

Ossification  of  the  Bones  of  the  Hand. — The  carpal  bones  are  each  ossified  from  a  single  center, 
and  ossification  proceeds  in  the  following  order  (Fig.  234) :    in  the  capitate  and  hamate,  during 


1 


THE  HIP  BONE  231 


the  first  year,  the  former  preceding  the  latter;  in  the  triangular,  during  the  third  year;  in  the 
lunate  and  greater  multangular,  during  the  fifth  year,  the  former  preceding  the  latter;  in  the 
navicular,  during  the  sixth  year;  in  the  lesser  multangular,  during  the  eighth  year;  and  in 
the  pisiform,  about  the  twelfth  year 

Occasionally  an  additional  bone,  the  os  centrale,  is  found  on  the  back  of  the  carpus,  lying 
between  the  navicular,  lesser  multangular,  and  capitate.  During  the  second  month  of  fetal  life 
it  is  represented  by  a  small  cartilaginous  nodule,  which  usually  fuses  with  the  cartilaginous  navic- 
ular. Sometimes  the  styloid  process  of  the  third  metacarpal  is  detached  and  forms  an  additional 
ossicle. 

The  metacarpal  bones  are  each  ossified  from  two  centers:  one  for  the  body  and  one  for  the 
distal  extremity  of  each  of  the  second,  third,  fourth,  and  fifth  bones;  one  for  the  body  and  one 
for  the  base  of  the  first  metacarpal  bone.^  The  first  metacarpal  bone  is  therefore  ossified  in  the 
same  manner  as  the  phalanges,  and  this  has  led  some  anatomists  to  regard  the  thumb  as  being 
made  up  of  three  phalanges,  and  not  of  a  metacarpal  bone  and  two  phalanges.  Ossification  com- 
mences in  the  middle  of  the  body  about  the  eighth  or  ninth  week  of  fetal  life,  the  centers  for  the 
second  and  third  metacarpals  being  the  first,  and  that  for  the  first  metacarpal,  the  last,  to  appear; 
about  the  third  year  the  distal  extremities  of  the  metacarpals  of  the  fingers,  and  the  base  of  the 
metacarpal  of  the  thumb,  begin  to  ossify;  they  unite  with  the  bodies  about  the  twentieth  year. 

The  phalanges  are  each  ossified  from  two  centers:  one  for  the  body,  and  one  for  the  proximal 
extremity.  Ossification  begins  in  the  body,  about  the  eighth  week  of  fetal  life.  Ossification  of 
the  proximal  extremity  commences  in  the  bones  of  the  first  row  between  the  third  and  fourth 
y(!ars,  and  a  year  later  in  those  of  the  second  and  third  rows.  The  two  centers  become  united 
in  each  row  between  the  eighteenth  and  twentieth  years. 

In  the  ungual  phalanges  the  centers  for  the  bodies  appear  at  the  distal  extremities  of  the 
phalanges,  instead  of  at  the  middle  of  the  bodies,  as  in  the  other  phalanges.  Moreover,  of  all 
the  bones  of  the  hand,  the  ungual  phalanges  are  the  first  to  ossify. 

THE  BONES  OF  THE  LOWER  EXTREMITY  (OSSA  EXTREMITATIS  INFERIORIS). 

The  Hip  Bone  (Os  Coxae;  Innominate  Bone). 

The  hip  bone  is  a  large,  flattened,  irregularly  shaped  bone,  constricted  in  the 
center  and  expanded  above  and  below.  It  meets  its  fellow  on  the  opposite  side 
ill  the  middle  line  in  front,  and  together  they  form  the  sides  and  anterior  wall  of 
tie  pelvic  cavity.  It  consists  of  three  parts,  the  ilium,  ischium,  and  pubis,  which 
are  distinct  from  each  other  in  the  young  subject,  but  are  fused  in  the  adult; 
t  tie  union  of  the  three  parts  takes  place  in  and  around  a  large  cup-shaped  articular 
cavity,  the  acetabulum,  which  is  situated  near  the  middle  of  the  outer  surface  of  the 
lone.  The  ilium,  so-called  because  it  supports  the  flank, is  the  superior  broad  and 
expanded  portion  which  extends  upward  from  the  acetabulum.  The  ischium  is  the 
lowest  and  strongest  portion  of  the  bone;  it  proceeds  downward  from  the  acetab- 
ilum,  expands  into  a  large  tuberosity,  and  then,  curving  forward,  forms,  with 
the  pubis,  a  large  aperture,  the  obturator  foramen.  The  pubis  extends  medialward 
and  downward  from  the  acetabulum  and  articulates  in  the  middle  line  with  the 
I  one  of  the  opposite  side:  it  forms  the  front  of  the  pelvis  and  supports  the  external 
crgans  of  generation.  ' 

The  niiim  {os  ilii). — ^The  ilium  is  divisible  into  two  parts,  the  body  and  the 
ala;  the  separation  is  indicated  on  the  internal  surface  by  a  curved  line,  the  arcuate 
Ime,  and  on  the  external  surface  by  the  margin  of  the  acetabuluni. 

The  Body  {corpus  oss.  ilii). — The  body  enters  into  the  formation  of  the  acetab- 
jlum,  of  which  it  forms  rather  less  than  two-fifths.  Its  external  surface  is  partly 
articular,  partly  non-articular;  the  articular  segment  forms  part  of  the  lunate 
surface  of  the  acetabulum,  the  non-articular  portion  contributes  to  the  acetabular 
fossa.  The  internal  surface  of  the  body  is  part  of  the  wall  of  the  lesser  pelvis  and 
gives  origin  to  some  fibers  of  the  Obturator  internus.  Below,  it  is  continuous  with 
the  pelvic  surfaces  of  the  ischium  and  pubis,  only  a  faint  line  indicating  the  place 
of  union. 


an 

■ 


Allen  Thomson  demonstrated  the  fact  that  the  first  metacarpal  bone  is  often  developed  from  three  centers:    that  is 
say,  there  is  a  separate  nucleus  for  the  distal  end,  forming  a  distinct  epiphysis  visible  at  the  age  of  seven  or  eight 
®*,'^,      .  .°  stated  that  there  are  traces  of  a  proximal  epiphysis  in  the  second  metacarpal  bone,  Journal  of  Anatomy 
and  Physiology,  1869. 


232 


OSTEOLOGY 


The  Ala  {ala  oss.  ilii). — The  ala  is  the  large  expanded  portion  which  bounds 
the  greater  pelvis  laterally.  It  presents  for  examination  two  surfaces — an  extei-nal 
and  an  internal — a  crest,  and  two  borders — an  anterior  and  a  posterior.  The 
external  surf  ace  (Fig.  235),  known  as  the  dorsum  ilii,  is  directed  backward  and  lateral- 
ward  behind,  and  downward  and  lateralward  in  front.  It  is  smooth,  convex  in  front, 


Posterior 

superio 

spine 


Posterior 
inferior 
spine 


Oemellus  superior 
JSpine  of  ischium 

Qemdlus  inferior 


Ant.  superior 
spine 


-Anterior  inferior  spine 

Articular  capsule 
Ligamentum  teres 


_    o/\       Rectus 
Fuhia]^^  abdominis 


Pyramidalis 

Adductor 
longus 


Fig.  235. — Right  hip  bone.     External  surface. 

deeply  concave  behind;  bounded  above  by  the  crest,  below  by  the  upper  border 
of  the  acetabulum,  in  front  and  behind  by  the  anterior  and  posterior  borders. 
This  surface  is  crossed  in  an  arched  direction  by  three  lines — the  posterior,  anterior,, 
and  inferior  gluteal  lines.  The  posterior  gluteal  line  {superior  curved  line),  the  short- 
est of  the  three,  begins  at  the  crest,  about  5  cm.  in  front  of  its  posterior  extremity; 
it  is  at  first  distinctly  marked,  but  as  it  passes  downward  to  the  upper  part  of  the 


THE  HIP  BONE 


233 


greater  sciatic  notch,  where  it  ends,  it  becomes  less  distinct,  and  is  often  altogether 
lost.  Behind  this  line  is  a  narrow  semilunar  surface,  the  upper  part  of  which 
is  rough  and  gives  origin  to  a  portion  of  the  Glutseus  maximus ;  the  lower  part  is 
smooth  and  has  no  muscular  fibers  attached  to  it.  The  anterior  gluteal  line  {middle 
curved  line),  the  longest  of  the  three,  begins  at  the  crest,  about  4  cm.  behind  its 
anterior  extremity,  and,  taking  a  curved  direction  downward  and  backward,  ends 


Levator  dm 


Constrictor  urethroe 

Cms  penis 
Via.  236. — Right  hip  bone.     Internal  surface. 


Transversus  perincei  superfic 
Ischiocavemosus 


at  the  upper  part  of  the  greater  sciatic  notch.  The  space  between  the  anterior 
and  posterior  gluteal  lines  and  the  crest  is  concave,  and  gives  origin  to  the  Glutseus 
medius.  Near  the  middle  of  this  line  a  nutrient  foramen  is  often  seen.  The 
inferior  gluteal  line  {inferior  curved  line),  the  least  distinct  of  the  three,  begins  in 
front  at  the  notch  on  the  anterior  border,  and,  curving  backward  and  downward, 
ends  near  the  middle  of  the  greater  sciatic  notch.    The  surface  of  bone  included 


234  OSTEOLOGY 


^IHR" 


between  the  anterior  and  inferior  gluteal  lines  is  concave  from  above  downward, 
convex  from  before  backward,  and  gives  origin  to  the  Glutseus  minimus.  Betwtien 
the  inferior  gluteal  line  and  the  upper  part  of  the  acetabulum  is  a  rough,  shallow 
groove,  from  which  the  reflected  tendon  of  the  Rectus  femoris  arises. 

The  internal  surface  (Fig.  236)  of  the  ala  is  bounded  above  by  the  crest,  below, 
by  the  arcuate  line;  in  front  and  behind,  by  the  anterior  and  posterior  borders. 
It  presents  a  large,  smooth,  concave  surface,  called  the  iliac  fossa,  which  gives 
origin  to  the  Iliacus  and  is  perforated  at  its  inner  part  by  a  nutrient  canal;  and 
below  this  a  smooth,  rounded  border,  the  arcuate  line,  which  runs  downward,  for- 
ward, and  medialward.  Behind  the  iliac  fossa  is  a  rough  surface,  divided  into  two 
portions,  an  anterior  and  a  posterior.  The  anterior  surface  {auricular  surface), 
so  called  from  its  resemblance  in  shape  to  the  ear,  is  coated  with  cartilage  in  the 
fresh  state,  and  articulates  with  a  similar  surface  on  the  side  of  the  sacrum. 
The  posterior  portion,  known  as  the  iliac  tuberosity,  is  elevated  and  rough,  for 
the  attachment  of  the  posterior  sacroiliac  ligaments  and  for  the  origins  of  the 
Sacrospinalis  and  Multifidus.  Below^  and  in  front  of  the  auricular  surface  is  the 
preauricular  sulcus,  more  commonly  present  and  better  marked  in  the  female 
than  in  the  male;  to  it  is  attached  the  pelvic  portion  of  the  anterior  sacroiliac 
ligament. 

The  crest  of  the  ilium  is  convex  in  its  general  outline  but  is  sinuously  curved, 
being  concave  inward  in  front,  concave  outward  behind.  It  is  thinner  at  the  center 
than  at  the  extremities,  and  ends  in  the  anterior  and  posterior  superior  iliac  spines. 
The  surface  of  the  crest  is  broad,  and  divided  into  external  and  internal  lips, 
and  an  intermediate  line.  About  5  cm.  behind  the  anterior  superior  iliac  spine 
there  is  a  prominent  tubercle  on  the  outer  lip.  To  the  external  lip  are  attached 
the  Tensor  fasciae  latse,  Obliquus  externus  abdominis,  and  Latissimus  dorsi,  and 
along  its  whole  length  the  fascia  lata;  to  the  intermediate  line  the  Obliquus  internus 
abdominis;  to  the  internal  lip,  the  fascia  iliaca,  the  Transversus  abdominis, 
Quadratus  lumborum,  Sacrospinalis,  and  Iliacus. 

The  anterior  border  of  the  ala  is  concave.  It  presents  two  projections,  separated 
by  a  notch.  Of  these,  the  uppermost,  situated  at  the  junction  of  the  crest  and 
anterior  border,  is  called  the  anterior  superior  iliac  spine;  its  outer  border  gives 
attachment  to  the  fascia  lata,  and  the  Tensor  fasciae  latse,  its  inner  border,  to  the 
Iliacus;  while  its  extremity  affords  attachment  to  the  inguinal  ligament  and  gives 
origin  to  the  Sartorius.  Beneath  this  eminence  is  a  notch  from  which  the  Sartorius 
takes  origin  and  across  which  the  lateral  femoral  cutaneous  nerve  passes.  Below 
the  notch  is  the  anterior  inferior  iliac  spine,  which  ends  in  the  upper  lip  of  the 
acetabulum;  it  gives  attachment  to  the  straight  tendon  of  the  Rectus  femoris  and 
to  the  iliofemoral  ligament  of  the  hip-joint.  Medial  to  the  anterior  inferior  spine 
is  a  broad,  shallow  groove,  over  which  the  Iliacus  and  Psoas  major  pass.  This 
groove  is  bounded  medially  by  an  eminence,  the  iliopectineal  eminence,  which 
marks  the  point  of  union  of  the  ilium  and  pubis. 

The  posterior  border  of  the  ala,  shorter  than  the  anterior,  also  presents  two 
projections  separated  by  a  notch,  the  posterior  superior  iliac  spine  and  the  posterior 
inferior  iliac  spine.  The  former  serves  for  the  attachment  of  the  oblique  portion 
of  the  posterior  sacroiliac  ligaments  and  the  Multifidus;  the  latter  corresponds 
with  the  posterior  extremity  of  the  auricular  surface.  Below  the  posterior  inferior 
spine  is  a  deep  notch,  the  greater  sciatic  notch. 

The  Ischium  {os  ischii). — The  ischium  forms  the  lower  and  back  part  of  the 
hip  bone.    It  is  divisible  into  three  portions — a  body  and  two  rami. 

The  Body  {corpus  oss.  ischii). — The  body  enters  into  and  constitutes  a  little 
more  than  two-fifths  of  the  acetabulum.  Its  external  surface  forms  part  of  the 
lunate  surface  of  the  acetabulum  and  a  portion  of  the  acetabular  fossa.  Its  internal 
surface  is  part  of  the  wall  of  the  lesser  pelvis;  it  gives  origin  to  some  fibers  of  the 


THE  HIP  BONE 


235 


Obturator  mternus.  Its  anterior  border  projects  as  the  posterior  obturator  tubercle; 
from  its  posterior  border  there  extends  backward  a  thin  and  pointed  triangular 
eminence,  the  ischial  spine,  more  or  less  elongated  in  different  subjects.  The 
external  surface  of  the  spine  gives  attachment  to  the  Gemellus  superior,  its  internal 
surface  to  the  Coccygeus,  Levator  ani,  and  the  pelvic  fascia;  while  to  the  pointed 
extremity  the  sacrospinous  ligament  is  attached.  Above  the  spine  is  a  large  notch, 
the  greater  sciatic  notch,  converted  into  a  foramen  by  the  sacrospinous  ligament; 
it  transmits  the  Piriformis,  the  superior  and  inferior  gluteal  vessels  and  nerves, 
the  sciatic  and  posterior  femoral  cutaneous  nerves,  the  internal  pudendal  vessels, 
and  nerve,  and  the  nerves  to  the  Obturator  internus  and  Quadratus  femoris.  Of 
these,  the  superior  gluteal  vessels  and  nerve  pass  out  above  the  Piriformis,  the 
other  structures  below  it.  Below  the  spine  is  a  smaller  notch,  the  lesser  sciatic 
notch;  it  is  smooth,  coated  in  the  recent  state  with  cartilage,  the  surface  of  which 
presents  two  or  three  ridges  corresponding  to  the  subdivisions  of  the  tendon  of 
the  Obturator  internus,  which  winds  over  it.  It  is  converted  into  a  foramen  by 
the  sacrotuberous  and  sacrospinous  ligaments,  and  transmits  the  tendon  of  the 
Obturator  internus,  the  nerve  which  supplies  that  muscle,  and  the  internal 
pudendal  vessels  and  rterve. 

The  Superior  Ramus  {ramus  superior  oss.  ischii;  descending  ramus). — The 
superior  ramus  projects  downward  and  backward  from  the  body  and  presents 
for  examination  three  surfaces:  external,  internal,  and  posterior.  The  external 
surface  is  quadrilateral  in  shape.  It  is  bounded  above  by  a  groove  which  lodges 
the  tendon  of  the  Obturator  externus;  below,  it  is  continuous  with  the  inferior 
ramus;  in  front  it  is  limited  by  the  posterior  margin  of  the  obturator  foramen; 
behind,  a  prominent  margin  separates  it  from  the  posterior  surface.  In  front  of 
this  margin  the  surface  gives  origin  to  the  Quadratus  femoris,  and  anterior  to  this 
to  some  of  the  fibers  of  origin  of  the  Obturator  externus;  the  lower  part  of  the  sur- 
iace  gives  origin  to  part  of  the  Adductor  magnus.  The  internal  surface  forms  part 
of  the  bony  wall  of  the  lesser  pelvis.  In  front  it  is  limited  by  the  posterior  margin 
of  the  obturator  foramen.  Below,  it  is  bounded  by  a  sharp  ridge  which  gives 
attachment  to  a  falciform  prolongation  of  the  sacrotuberous  ligament,  and,  more 
anteriorly,  gives  origin  to  the  Transversus  perinsei  and  Ischiocavernosus.  Poste- 
liorly  the  ramus  forms  a  large  swelling,  the  tuberosity  of  the  ischium,  which  is  divided 
into  two  portions:  a  lower,  rough,  somewhat  triangular  part,  and  an  upper,  smooth, 
juadrilateral  portion.  The  lower  portion  is  subdivided  by  a  prominent  longitudinal 
:*idge,  passing  from  base  to  apex,  into  two  parts;  the  outer  gives  attachment  to 
"he  Adductor  magnus,  the  inner  to  the  sacrotuberous  ligament.  The  upper  portion 
s  subdivided  into  two  areas  by  an  oblique  ridge,  which  runs  downward  and  out- 
ward; from  the  upper  and  outer  area  the  Semimembranosus  arises;  from  the  lower 
and  inner,  the  long  head  of  the  Biceps  femoris  and  the  Semitendinosus. 

The  Inferior  Ramus  {ramus  inferior  oss.  ischii;  ascending  ramus). — The  inferior 
ramus  is  the  thin,  flattened  part  of  the  ischium,  which  ascends  from  the  superior 
ramus,  and  joins  the  inferior  ramus  of  the  pubis — the  junction  being  indicated  in 
the  adult  by  a  raised  line.  The  outer  surface  is  uneven  for  the  origin  of  the  Obturator 
externus  and  some  of  the  fibers  of  the  Adductor  magnus;  its  inner  surface  forms 
part  of  the  anterior  wall  of  the  pelvis.  Its  medial  border  is  thick,  rough,  slightly 
everted,  forms  part  of  the  outlet  of  the  pelvis,  and  presents  two  ridges  and  an 
intervening  space.  The  ridges  are  continuous  with  similar  ones  on  the  inferior 
tamus  of  the  pubis :  to  the  outer  is  attached  the  deep  layer  of  the  superficial  peri- 
heal  fascia  {fascia  of  Colles),  and  to  the  inner  the  inferior  fascia  of  the  urogenital 
diaphragm.  If  these  two  ridges  be  traced  downward,  they  will  be  found  to  join 
i«^^ith  each  other  just  behind  the  point  of  origin  of  the  Transversus  periniei;  here 

She  two  layers  of  fascia  are  continuous  behind  the  posterior  border  of  the  muscle. 
^o  the  intervening  space,  just  in  front  of  the  point  of  junction  of  the  ridges,  the 


236  ^^^^^^^       OSTEOLOGY 


Transversus  perinan  is  attached,  and  in  front  of  this  a  portion  of  the  cms  penis 
vel  clitoridis  and  the  Ischiocavernosus.  Its  lateral  border  is  thin  and  sharp,  and 
forms  part  of  the  medial  margin  of  the  obturator  foramen. 

The  Pubis  {os  imbis) . — The  pubis,  the  anterior  part  of  the  hip  bone,  is  divisible 
into  a  body,  a  superior  and  an  inferior  ramus. 

The  Body  {corpus  oss.  pubis). — The  body  forms  one-fifth  of  the  acetabulum, 
contributing  by  its  external  surface  both  to  the  lunate  surface  and  the  acetabular 
fossa.  Its  internal  surface  enters  into  the  formation  of  the  wall  of  the  lesser  peh'is 
and  gives  origin  to  a  portion  of  the  Obturator  internus. 

The  Superior  Ramus  {ramus  superior  oss.  pubis;  ascending  ramus) . — The  superior 
ramus  extends  from  the  body  to  the  median  plane  where  it  articulates  with  its 
fellow  of  the  opposite  side.  It  is  conveniently  described  in  two  portions,  viz.,  a 
medial  flattened  part  and  a  narrow  lateral  prismoid  portion. 

The  Medial  Portion  of  the  superior  ramus,  formerly  described  as  the  body  of 
the  pubis,  is  somewhat  quadrilateral  iil  shape,  and  presents  for  examination  two 
surfaces  and  three  borders.  The  anterior  surface  is  rough,  directed  downward  and 
outward,  and  serves  for  the  origin  of  various  muscles.  The  Adductor  longus  arises 
from  the  upper  and  medial  angle,  immediately  below  the  crest;  lower  down,  the 
Obturator  externus,  the  Adductor  brevis,  and  the  upper  part  of  the  Gracilis  take 
origin.  The  posterior  surface,  convex  from  above  downward,  concave  from  side 
to  side,  is  smooth,  and  forms  part  of  the  anterior  wall  of  the  pelvis.  It  gives  origin 
to  the  Levator  ani  and  Obturator  internus,  and  attachment  to  the  puboprostatic 
ligaments  and  to  a  few  muscular  fibers  prolonged  from  the  bladder.  The  upper 
border  presents  a  prominent  tubercle,  the  pubic  tubercle  {pubic  spine),  which  pro- 
jects forward;  the  inferior  crus  of  the  subcutaneous  inguinal  ring  {external  abdominal 
ring),  and  the  inguinal  ligament  {Pouparfs  ligament)  are  attached  to  it.  Passing 
upward  and  lateralward  from  the  pubic  tubercle  is  a  well-defined  ridge,  forming 
a  part  of  the  pectineal  line  which  marks  the  brim  of  the  lesser  pelvis:  to  it  are 
attached  a  portion  of  the  inguinal  falx  {conjoined  tendon  of  Obliquus  internus 
and  Transversus),  the  lacunar  ligament  {Gimbernafs  ligament),  and  the  reflected 
inguinal  ligament  {triangular  fascia).  Medial  to  the  pubic  tubercle  is  the  crest, 
which  extends  from  this  process  to  the  medial  end  of  the  bone.  It  affords  attach- 
ment to  the  inguinal  falx,  and  to  the  Rectus  abdominis  and  Pyramidalis.  The 
point  of  junction  of  the  crest  with  the  medial  border  of  the  bone  is  called  the  angle ; 
to  it,  as  well  as  to  the  symphysis,  the  superior  crus  of  the  subcutaneous  inguinal 
ring  is  attached.  The  medial  border  is  articular;  it  is  oval,  and  is  marked  by  eight 
or  nine  transverse  ridges,  or  a  series  of  nipple-like  processes  arranged  in  rows, 
separated  by  grooves;  they  serve  for  the  attachment  of  a  thin  layer  of  cartilage, 
which  intervenes  between  it  and  the  interpubic  fibrocartilaginous  lamina.  The 
lateral  border  presents  a  sharp  margin,  the  obturator  crest,  which  forms  part  of  the 
circumference  of  the  obturator  foramen  and  affords  attachment  to  the  obturator 
membrane. 

The  Lateral  Portion  of  the  ascending  ramus  has  three  surfaces :  superior,  inferior, 
and  posterior.  The  superior  surface  presents  a  continuation  of  the  pectineal  line, 
already  mentioned  as  commencing  at  the  pubic  tubercle.  In  front  of  this  line,  the 
surface  of  bone  is  triangular  in  form,  wider  laterally  than  medially,  and  is  covered 
by  the  Pectineus.  The  surface  is  bounded,  laterally,  by  a  rough  eminence,  the 
iliopectineal  eminence,  which  serves  to  indicate  the  point  of  junction  of  the  ilium 
and  pubis,  and  below  by  a  prominent  ridge  which  extends  from  the  acetabular 
notch  to  the  pubic  tubercle.  The  inferior  surface  forms  the  upper  boundary  of 
the  obturator  foramen,  and  presents,  laterally,  a  broad  and  deep,  oblique  groove, 
for  the  passage  of  the  obturator  vessels  and  nerve;  and  medially,  a  sharp  margin, 
the  obturator  crest,  forming  part  of  the  circumference  of  the  obturator  foramen, 
and  giving  attachment  to  the  obturator  membrane.    The  posterior  surface  consti- 


THE  HIP  BONE 


lutes  part  of  the  anterior  boundary  of  the  lesser  pelvis.  It  is  smooth,  convex  from 
above  downward,  and  affords  origin  to  some  fibers  of  the  Obturator  internus. 

The  Inferior  Ramus  {ramus  inferior  oss.  pubis;  descending  ramus). — The  inferior 
ramus  is  thin  and  flattened.  It  passes  lateralward  and  downward  from  the  medial 
end  of  the  superior  ramus;  it  becomes  narrower  as  it  descends  and  joins  with  the 
inferior  ramus  of  the  ischium  below  the  obturator  foramen.  Its  anterior  surface 
is  rough,  for  the  origin  of  muscles — the  Gracilis  along  its  medial  border,  a  portion 
of  the  Obturator  externus  where  it  enters  into  the  formation  of  the  obturator 
foramen,  and  between  these  two,  the  Adductores  brevis  and  magnus,  the  former 
being  the  more  medial.  The  posterior  surface  is  smooth,  and  gives  origin  to  the 
Obturator  internus,  and,  close  to  the  medial  margin,  to  the  Constrictor  urethra?. 
The  medial  border  is  thick,  rough,  and  everted,  especially  in  females.  It  presents 
two  ridges,  separated  by  an  intervening  space.  The  ridges  extend  downward,  and 
are  continuous  with  similar  ridges  on  the  inferior  ramus  of  the  ischium;  to  the 
external  is  attached  the  fascia  of  Colles,  and  to  the  internal  the  inferior  fascia  of 
the  urogenital  diaphragm.  The  lateral  border  is  thin  and  sharp,  forms  part  of  the 
circumference  of  the  obturator  foramen,  and  gives  attachment  to  the  obturator 
membrane. 

The  Acetabulum  (cotyloid  cavity) . — The  acetabulum  is  a  deep,  cup-shaped,  hemi- 
spherical depression,  directed  downward,  lateralward,  and  forward.  It  is  formed 
medially  by  the  pubis,  above  by  the  ilium,  laterally  and  below  by  the  ischium; 
a  little  less  than  two-fifths  is  contributed  by  the  ilium,  a  little  more  than  two- 
lifths  by  the  ischium,  and  the  remaining  fifth  by  the  pubis.  It  is  bounded  by  a 
])rominent  uneven  rim,  which  is  thick  and  strong  above,  and  serves  for  the  attach- 
ment of  the  glenoidal  labrum  (cotyloid  ligament),  which  contracts  its  orifice,  and 
deepens  the  surface  for  articulation.  It  presents  below  a  deep  notch,  the  acetabular 
notch,  which  is  continuous  with  a  circular  non-articular  depression,  the  acetabular 
riossa,  at  the  bottom  of  the  cavity:  this  depression  is  perforated  by  numerous 
[apertures,  and  lodges  a  mass  of  fat.  The  notch  is  converted  into  a  foramen  by 
l^e  transverse  ligament;  through  the  foramen  nutrient  vessels  and  nerves  enter 
[the  joint;  the  margins  of  the  notch  serve  for  the  attachment  of  the  ligamentum 
teres.  The  rest  of  the  acetabulum  is  formed  by  a  curved  articular  surface,  the 
lunate  surface,  for  articulation  with  the  head  of  the  femur. 

The  Obturator  Foramen  (foramen  ohturatum;  thyroid  foramen). — The  obturator 
foramen  is  a  large  aperture,  situated  between  the  ischium  and  pubis.  In  the  male 
it  is  large  and  of  an  oval  form,  its  longest  diameter  slanting  obliquely  from  before 
backward;  in  the  female  it  is  smaller,  and  more  triangular.  It  is  bounded  by  a 
thin,  uneven  margin,  to  which  a  strong  membrane  is  attached,  and  presents, 
I  superiorly,  a  deep  groove,  the  obturator  groove,  which  runs  from  the  pelvis  obliquely 
medialward  and  downward.  This  groove  is  converted  into  a  canal  by  a  ligamentous 
band,  a  specialized  part  of  the  obturator  membrane,  attached  to  two  tubercles: 
one,  the  posterior  obturator  tubercle,  on  the  medial  border  of  the  ischium,  just  in 
front  of  the  acetabular  notch;  the  other,  the  anterior  obturator  tubercle,  on  the 
obturator  crest  of  the  superior  ramus  of  the  pubis.  Through  the  canal  the 
1  obturator  vessels  and  nerve  pass  out  of  the  pelvis. 

Structure. — The  thicker  parts  of  the  bone  consist  of  cancellous  tissue,  enclosed  between  two 
[layers  of  compact  tissue;  the  thinner  parts,  as  at  the  bottom  of  the  acetabulum  and  center  of 
[the  ihac  fossa,  are  usually  semitransparent,  and  composed  entirely  of  compact  tissue. 

Ossification  (Fig.  237). — The  hip  bone  is  ossified  from  eight  .centers:  three  primary — one  each 
for  the  ihum,  ischium,  and  pubis;  and  ^ye  secondary — one  each  for  the  crest  of  the  ilium,  the 
anterior  inferior  spine  (said  to  occur  more  frequently  in  the  male  than  in  the  female),  the  tuberosity 
lof  the  ischium,  the  pubic  symphysis  (more  frequent  in  the  female  than  in  the  male),  and  one  or 
Imore  for  the  Y-shaped  piece  at  the  bottom  of  the  acetabulum.  The  centers  appear  in  the  foUow- 
ling  order:  in  the  lower  part  of  the  ihum,  immediately  above  the  greater  sciatic  notch,  about 
I  the  eighth  or  ninth  week  of  fetal  life;  in  the  superior  ramus  of  the  ischium,  about  the  third  month; 


238 


OSTEOLOGY 


k 


in  the  superior  ramus  of  the  pubis,  between  the  fourth  and  fifth  months.  At  birth,  the  three 
primary  centers  are  quite  separate,  the  crest,  the  bottom  of  the  acetabulum,  the  ischial  tuberosity, 
and  the  inferior  rami  of  the  ischium  and  pubis  being  still  cartilaginous.  By  the  seventh  or  eighth 
year,  the  inferior  rami  of  the  pubis  and  ischium  are  almost  completely  united  by  bone.  About 
the  thirteenth  or  fourteenth  year,  the  three  primary  centers  have  extended  their  growth  into  the 
bottom  of  the  acetabulum,'  and  are  there  separated  from  each  other  by  a  Y-shaped  portion  of 
cartilage,  which  now  presents  traces  of  ossification,  often  by  two  or  more  centers.  One  of  these, 
the  OS  acetabuli,  appears  about  the  age  of  twelve,  between  the  ilium  and  pubis,  and  fuses  with  them 
about  the  age  of  eighteen;  it  forms  the  pubic  part  of  the  acetabulum.  The  iUum  and  ischium 
then  become  joined,  and  lastly  the  pubis  and  ischium,  through  the  intervention  of  this  Y-shaped 
portion.  At  about  the  age  of  puberty,  ossification  takes  place  in  each  of  the  remaining  porti(ms, 
and  they  join  with  the  rest  of  the  bone  between  the  twentieth  and  twenty-fifth  years.  Separate 
centers  are  frequently  found  for  the  pubic  tubercle  and  the  ischial  spine,  and  for  the  crest  and 
angle  of  the  pubis. 

Articulations. — The  hip  bone  articulates  with  its  fellow  of  the  opposite  side,  and  with  the 
sacrum  and  femur. 

By  eight  centers  \  ^^''^^  primary  {Ilium.  lacUum.  and  Pvhia) 
.  "     "  I  Five  secondary 


(J.      ^^^''^^i* 


i'.Tui'*' 


Fig.  237. — Plan  of  ossification  of  the  hip  bone.    The  three  primary  centers  unite  through  a  Y-shaped  piece  about 
puberty.     Epiphyses  appear  about  puberty,  and  unite  about  twenty-fifth  year. 

The  Pelvis. 

The  pelvis,  so  called  from  its  resemblance  to  a  basin,  is  a  bony  ring,  interposed 
between  the  movable  vertebrae  of  the  vertebral  column  which  it  supports,  and  the 
lower  limbs  upon  which  it  rests;  it  is  stronger  and  more  massively  constructed 
than  the  wall  of  the  cranial  or  thoracic  cavities,  and  is  composed  of  four  bones: 
the  two  hip  bones  laterally  and  in  front  and  the  sacrum  and  cocc3rx  behind. 

The  pelvis  is  divided  by  an  oblique  plane  passing  through  the  prominence  of 
the  sacrum,  the  arcuate  and  pectineal  lines,  and  the  upper  margin  of  the  symphysis 
pubis,  into  the  greater  and  the  lesser  pelvis.  The  circumference  of  this  plane  is 
termed  the  linea  terminaUs  or  pelvic  brim. 

The  Greater  or  False  Pelvis  (pelvis  major). — The  greater  pelvis  is  the  expanded 
portion  of  the  cavity  situated  above  and  in  front  of  the  pelvic  brim.  It  is  bounded 
on  either  side  by  the  ilium;  in  front  it  is  incomplete,  presenting  a  wide  interval 
between  the  anterior  borders  of  the  ilia,  which  is  filled  up  in  the  fresh  state  by 


THE  PELVIS 


239 


the  parietes  of  the  abdomen;  behind  is  a  deep  notch  on  either  side  between  the  ilium 
and  the  base  of  the  sacrum."  It  supports  the  intestines,  and  transmits  part  of  their 
weight  to  the  anterior  wall  of  the  abdomen. 

The  Lesser  or  True  Pelvis  {pelvis  minor). — The  lesser  pelvis  is  that  part  of  the 
pelvic  cavity  which  is  situated  below  and  behind  the  pelvic  brim.  Its  bony  walls 
are  more  complete  than  those  of  the  greater  pehis.  For  convenience  of  descrip- 
tion, it  is  divided  into  an  inlet  bounded  by  the  superior  circumference,  and  outlet 
bounded  by  the  inferior  circumference,  and  a  cavity. 

The  Superior  Circumference. — The  superior  circumference  forms  the  brim  of  the 
pelvis,  the  included  space  being  called  the  superior  aperture  or  inlet  (apertura  pelvis 
[yninoris]  superior)  (Fig.  238).  It  is  formed  laterally  by  the  pectineal  and  arcuate 
lines,  in  front  by  the  crests  of  the  pubes,  and  behind  by  the  anterior  margin  of  the 
base  of  the  sacrum  and  sacrovertebral  angle.  The  superior  aperture  is  somewhat 
heart-shaped,  obtusely  pointed  in  front,  diverging  on  either  side,  and  encroached 
upon  behind  by  the  projection  forward  of  the  promontory  of  the  sacrum.  It  has 
three  principal  diameters:  antero-posterior,  transverse,  and  oblique.  The  antero- 
posterior or  conjugate  diameter  extends  from  the  sacrovertebral  angle  to  the  sym- 


fi 

I 


I 


Fig.  238. — Diameters  of  superior  aperture  of  lesser  pelvis  (female). 

physis  pubis;  its  average  measurement  is  about  110  mm.  in  the  female.  The 
t'ansverse  diameter  extends  across  the  greatest  width  of  the  superior  aperture, 
from  the  middle  of  the  brim  on  one  side  to  the  same  point  on  the  opposite;  its  aver- 
age measurement  is  about  135  mm.  in  the  female.  The  oblique  diameter  extends 
from  the  iliopectineal  eminence  of  one  side  to  the  sacroiliac  articulation  of  the 

pposite  side;  its  average  measurement  is  about  125  mm.  in  the  female. 
The  cavity  of  the  lesser  pelvis  is  bounded  in  front  and  below  by  the  pubic  sym- 

'hysis  and  the  superior  rami  of  the  pubes;  above  and  behind,  by  the  pelvic  surfaces 
of  the  sacrum  and  coccyx,  which,  cijrving  forward  above  and  below,  contract 
the  superior  and  inferior  apertures  of  the  cavity;  laterally,  by  a  broad,  smooth, 
quadrangular  area  of  bone,  corresponding  to  the  inner  surfaces  of  the  body  and 
superior  ramus  of  the  ischium  and  that  part  of  the  ilium  which  is  below  the  arcuate 
line.  From  this  description  it  will  be  seen  that  the  cavity  of  the  lesser  pelvis 
hi  a  short,  curved  canal,  considerably  deeper  on  its  posterior  than  on  its  anterior 
v/all.  It  contains,  in  the  fresh  subject,  the  pelvic  colon,  rectum,  bladder,  and  some 
of  the  organs  of  generation.  The  rectum  is  placed  at  the  back  of  the  pelvis,  in 
the  curve  of  the  sacrum  and  coccyx;  the  bladder  is  in  front,  behind  the  pubic  sym- 
physis. In  the  female  the  uterus  and  vagina  occupy  the  interval  between  these  viscera. 


240 


OSTEOLOGY 


The  Lower  Circumference. — The  lower  circumference  of  the  pelvis  is  very  irregu  ar; 
the  space  enclosed  by  it  is  named  the  inferior  aperture  or  outlet  {apertura  pelvis 
[minoris]  inferior)  (Fig.  239),  and  is  bounded  behind  by  the  point  of  the  coccyx, 
and  laterally  by  the  ischial  tuberosities.  These  eminences  are  separated  by  three 
notches:  one  in  front,  the  pubic  arch,  formed  by  the  convergence  of  the  inferior 


Fia.  239. — Diameters  of  inferior  aperture  of  lesser  pelvis  (female). 

rami  of  the  ischium  and  pubis  on  either  side.  The  other  notches,  one  on  either 
side,  are  formed  by  the  sacrum  and  coccyx  behind,  the  ischium  in  front,  and 
the  ilium  above;  they  are  called  the  sciatic  notches;  in  the  natural  state  they  are 
converted  into  foramina  by  the  sacrotuberous  and  sacrospinous  ligaments.  When 
the  ligaments  are  in  situ,  the  inferior  aperture  of  the  pelvis  is  lozenge-shaped, 

bounded,  in  front,  by  the  pubic  arcuate  ligament 
and  the  inferior  rami  of  the  pubes  and  ischia;  later- 
ally, by  the  ischial  tuberosities;  and  behind,  by  the 
sacrotuberous  ligaments  and  the  tip  of  the  coccyx. 

The  diameters  of  the  outlet  of  the  pelvis  are  two, 
antero-posterior  and  transverse.  The  antero-posterior 
diameter  extends  from  the  tip  of  the  coccyx  to  the 
lower  part  of  the  pubic  symphysis;  its  measurement 
is  from  90  to  115  mm.  in  the  female.  It  varies  with 
the  length  of  the  coccyx,  and  is  capable  of  increase 
or  diminution,  on  account  of  the  mobility  of  that 
bone.  The  transverse  diameter,  measured  between 
the  posterior  parts  of  the  ischial  tuberosities,  is  about 
115  mm.  in  the  female.* 

Axes  (Fig.  240). — A  Hne  at  right  angles  to  the  plane 
of  the  superior  aperture  at  its  center  would,  if  prolonged, 
pass  through  the  umbilicus  above  and  the  middle 
of  the  coccyx  below ;  the  axis  of  the  superior  aperture 
is  therefore  directed  downward  and  backward.  The 
axis  of  the  inferior  aperture,  produced  upward,  would 
touch  the  base  of  the  sacrum,  and  is  also  directed 
downward,  and  slightly  backward.  The  axis  of  the  cavity — i.  e.,  an  axis  at  right 
angles  to  a  series  of  planes  between  those  of  the  superior  and  inferior  apertures 

'  The  measurements  of  the  pelvis  given  above  are  fairly  accurate,  but  different  figures  are  given  by  various  authors 
no  doubt  due  mainly  to  differences  in  the  physique  and  stature  of  the  population  from  whom  the  measurements  have 
been  taken. 


Fia.  240. 


-Median  sagittal  section  of 
pelvis. 


— is  curved  like  the  cavity  itself:  this  curve  corresponds  to  the  concavity  of  the 
sacrum  and  coccyx,  the  extremities  being  indicated  by  the  central  points  of  the 
superior  and  inferior  apertures.  A  knowledge  of  the  direction  of  these  axes 
serves  to  explain  the  course  of  the  fetus  in  its  passage  through  the  pelvis  during 
parturition. 

Position  of  the  Pelvis  (Fig.  240). — In  the  erect  posture,  the  pelvis  is  placed 
obliquely  with  regard  to  the  trunk :  the  plane  of  the  superior  aperture  forms  an 
angle  of  from  50°  to  60°,  and  that  of  the  inferior  aperture  one  of  about  15°  with 
the  horizontal  plane.  The  pelvic  surface  of  the  symphysis  pubis  looks  upward 
and  backward,  the  concavity  of  the  sacrum  and  coccyx  downward  and  forward. 
The  position  of  the  pelvis  in  the  erect  posture  may  be  indicated  by  holding  it  so 
that  the  anterior  superior  iliac  spines  and  the  front  of  the  top  of  the  symphysis 
pubis  are  in  the  same  vertical  plane. 


Fig.   241. — Male  pelvis. 


Differences  between  the  Male  and  Female  Pelves. — The  female  pelvis  (Fig. 
1'42)  is  distinguished  from  that  of  the  male  (Fig.  241)  by  its  bones  being  more 
<lelicate  and  its  depth  less.  The  whole  pelvis  is  less  massive,  and  its  muscular 
impressions  are  slightly  marked.  The  ilia  are  less  sloped,  and  the  anterior  iliac 
opines  more  widely  separated;  hence  the  greater  lateral  prominence  of  the  hips. 
The  preauricular  sulcus  is  more  commonly  present  and  better  marked.  The  supe- 
rior aperture  of  the  lesser  pelvis  is  larger  in  the  female  than  in  the  male;  it  is  more 
nearly  circular,  and  its  obliquity  is  greater.  The  cavity  is  shallower  and  wider; 
the  sacrum  is  shorter  wider,  and  its  upper  part  is  less  curved;  the  obturator 
1  bramina  are  triangular  in  shape  and  smaller  in  size  than  in  the  male.  The  inferior 
aperture  is  larger  and  the  coccyx  more  movable.  The  sciatic  notches  are  wider 
and  shallower,  and  the  spines  of  the  ischia  project  less  inward.  The  acetabula 
are  smaller  and  look  more  distinctly  forward  (Derry^).  The  ischial  tuberosities 
and  the  acetabula  are  wider  apart,  and  the  former  are  more  everted.  The  pubic 
^symphysis  is  less  deep,  and  the  pubic  arch  is  wider  and  more  rounded  than  in  the 
male,  where  it  is  an  angle  rather  than  an  arch. 


16 


'  Journal  of  Anatomy  and  Physiology,  vol.  xliii. 


242 


OSTEOLOGY 


The  size  of  the  pelvis  varies  not  only  in  the  two  sexes,  but  also  in  diffen 
members  of  the  same  sex,  and  does  not  appear  to  be  influenced  in  any  way  by  the 
height  of  the  individual.  Women  of  short  stature,  as  a  rule,  have  broad  pelves. 
Occasionally  the  pelvis  is  equally  contracted  in  all  its  dimensions,  so  much  so 
that  all  its  diameters  measure  12.5  mm.  less  than  the  average,  and  this  even  in 
well-formed  women  of  average  height.  The  principal  divergences,  however,  are 
found  at  the  superior  aperture,  and  affect  the  relation  of  the  antero-posterior 
to  the  transverse  diameter.  Thus  the  superior  aperture  may  be  elliptical  either 
in  a  transverse  or  an  antero-posterior  direction,  the  transverse  diameter  in  the 
former,  and  the  antero-posterior  in  the  latter,  greatly  exceeding  the  other  diameters; 
in  other  instances  it  is  almost  circular. 


Fig.  242. — Female  pelvis. 

In  the  fetus,  and  for  several  years  after  birth,  the  pelvis  is  smaller  in  proportion 
than  in  the  adult,  and  the  projection  of  the  sacrovertebral  angle  less  marked. 
The  characteristic  differences  between  the  male  and  female  pelvis  are  distinctly 
indicated  as  early  as  the  fourth  month  of  fetal  life. 

Abnormalities. — There  is  arrest  of  development  in  the  bones  of  the  pelvis  in  cases  of  extro- 
version of  the  bladder;  the  anterior  part  of  the  pelvic  girdle  is  deficient,  the  superior  rami  of 
the  pubes  are  imperfectly  developed,  and  the  symphysis  is  absent.  "The  pubic  bones  are  sepa- 
rated to  the  extent  of  from  two  to  four  inches,  the  superior  rami  shortened  and  directed  forward, 
and  the  obturator  foramen  diminished  in  size,  narrowed,  and  turned  outward.  The  iliac  bones 
are  straightened  out  more  than  normal.  The  sacrum  is  very  peculiar.  The  lateral  curve,  instead 
of  being  concave,  is  flattened  out  or  even  convex,  with  the  iliosacral  facets  turned  more  outward 
than  normal,  while  the  vertical  curve  is  straightened."^ 


The  Femur  (Thigh  Bone). 

The  femur  (Figs.  244,  245),  the  longest  and  strongest  bone  in  the  skeleton,  is 
almost  perfectly  cylindrical  in  the  greater  part  of  its  extent.  In  the  erect  posture 
it  is  not  vertical,  being  separated  above  from  its  fellow  by  a  considerable  interval, 
which  corresponds  to  the  breadth  of  the  pelvis,  but  inclining  gradually  downward 
and  medialward,  so  as  to  approach  its  fellow  toward  its  lower  part,  for  the  purpose 
of  bringing  the  knee-joint  near  the  line  of  gravity  of  the  body.  The  degree  of  this 
inclination  varies  in  different  persons,  and  is  greater  in  the  female  than  in  the  male, 

'  Wood,  Heath's  Dictionary  of  Practical  Surgery,  i,  426. 


THE  FEMUR 


243 


on  account  of  the  greater  breadth  of  the  pelvis.  The  femur,  like  other  long  bones, 
is  divisible  into  a  body  and  two  extremities. 

The  Upper  Extremity  {yroximal  extremity,  Fig.  243). — The  upper  extremity 
presents  for  examination  a  head,  a  neck,  a  greater  and  a  lesser  trochanter. 

The  Head  {caput  femoris) .■ — The  head  which  is  globular  and  forms  rather  more 
than  a  hemisphere,  is  directed  upward,  medialward,  and  a  little  forward,  the  greater 
part  of  its  convexity  being  above  and  in  front.  Its  surface  is  smooth,  coated  with 
cartilage  in  the  fresh  state,  except  over  an  ovoid  depression,  the  fovea  capitis 
femoris,  which  is  situated  a  little  below  and  behind  the  center  of  the  head,  and  gives 
attachment  to  the  ligamentum  teres. 

The  Neck  (collum  femoris) . — The  neck  is  a  flattened  pyramidal  process  of  bone, 
connecting  the  head  with  the  body,  and  forming  with  the  latter  a  wide  angle  open- 
ing medialward.  The  angle  is  widest  in  infancy,  and  becomes  lessened  during 
growth,  so  that  at  puberty  it  forms  a  gentle  curve  from  the  axis  of  the  body  of  the 
bone.  In  the  adult,  the  neck  forms  an  angle  of  about  125°  with  the  body,  but  this 
varies  in  inverse  proportion  to  the  development  of  the  pelvis  and  the  stature.    In 


Fovea  capitis, 
for  lig.  teres 


Obturator  internus  and  Gemelli 

Pirifor/mis 

Insertion  of  Obturator 
externum 


Oreater  trocJmnter 


Lesser  trochanter 


Fig.  243. — Upper  e.\tremity  of  right  femur  viewed  from  behind  and  above. 


the  female,  in  consequence  of  the  increased  width  of  the  pelvis,  the  neck  of  the 
femur  forms  more  nearly  a  right  angle  with  the  body  than  it  does  in  the  male. 
^^he  angle  decreases  during  the  period  of  growth,  but  after  full  growth  has  been 
attained  it  does  not  usually  undergo  any  change,  even  in  old  age;  it  varies  con- 
siderably in  different  persons  of  the  same  age.  It  is  smaller  in  short  than  in  long 
bones,  and  when  the  pelvis  is  wide.  In  addition  to  projecting  upward  and  medial- 
V7ard  from  the  body  of  the  femur,  the  neck  also  projects  somewhat  forward ;  the 
amount  of  this  forward  projection  is  extremely  variable,  but  on  an  average  is  from 
12°  to  14°. 

The  neck  is  flattened  from  before  backward,  contracted  in  the  middle,  and 
broader  laterally  than  medially.  The  vertical  diameter  of  the  lateral  half  is  in- 
creased by  the  obliquity  of  the  lower  edge,  which  slopes  downward  to  join  the 
body  at  the  level  of  the  lesser  trochanter,  so  that  it  measures  one-third  more 
than  the  antero-posterior  diameter.  The  medial  half  is  smaller  and  of  a  more 
circular  shape.  The  anterior  sm-f ace  of  the  neck  is  perforated  by  numerous  vascular 
foramina.  Along  the  upper  part  of  the  line  of  junction  of  the  anterior  surface 
with   the    head    is    a  shallow   groove,   best  marked    in    elderly    subjects;    this 


I 


244 


OSTEOLOGY 


Obturator  internus 
and  Oemelli 
Piriformis 


Tubercle 


Articular  capsule 


Articvlar  capsule 


Adductor 
tvbercle 

Medial 
Cpicondyle 


Fio.  244. — Right  femur.     Anterior  surface. 


groove  lodges  the  orbicular  fibers 
of  the  capsule  of  the  hip-joint. 
The  posterior  surface  is  smooth,  and 
is  broader  and  more  concave  than 
the  anterior:  the  posterior  part  of 
the  capsule  of  the  hip-joint  is 
attached  to  it  about  1  cm.  above 
the  intertrochanteric  crest.  The 
superior  border  is  short  and  thick, 
and  ends  laterally  at  the  greater 
trochanter;  its  surface  is  perforated 
by  large  foramina.  The  inferior 
border,  long  and  narrow,  curves  a 
little  backward,  to  end  at  the  lesser 
trochanter. 

The  Trochanters.^ — The  trochan- 
ters are  prominent  processes  which 
afford  leverage  to  the  muscles  that 
rotate  the  thigh  on  its  axis.  They 
are  two  in  number,  the  greater  and 
the  lesser. 

The  Greater  Trochanter  {trochanter 
major;  great  trochanter)  is  a  large, 
irregular,  quadrilateral  eminence, 
situated  at  the  junction  of  the  neck 
with  the  upper  part  of  the  body.  It 
is  directed  a  little  lateralward  and 
backward,  and,  in  the  adult,  is  about 
1  cm.  lower  than  the  head.  It  has 
two  surfaces  and  four  borders.  The 
lateral  surface,  quadrilateral  in  form, 
is  broad,  rough,  convex,  and  marked 
by  a  diagonal  impression,  which 
extends  from  the  postero-superior 
to  the  antero-inferior  angle,  and 
serves  for  the  insertion  of  the  ten- 
don of  the  Glutaeus  medius.  Above 
the  impression  is  a  triangular  sur- 
face, sometimes  rough  for  part  of 
the  tendon  of  the  same  muscle, 
sometimes  smooth  for  the  inter- 
position of  a  bursa  between  the 
tendon  and  the  bone.  Below  and 
behind  the  diagonal  impression  is 
a  smooth,  triangular  surface,  over 
which  the  tendon  of  the  Glutseus 
maximus  plays,  a  bursa  being  inter- 
posed. The  medial  surface,  of  much 
less  extent  than  the  lateral,  pre- 
sents at  its  base  a  deep  depression, 
the  trochanteric  fossa  (digital  fossa), 
for  the  insertion  of  the  tendon  of 
the  Obturator  externus,  and  above 
and  in  front  of  this  an  impression 
for    the   insertion  of   the  Obtura- 


tor  internus  and  Gemelli.  The 
superior  border  is  free;  it  is  thick 
and  irregular,  and  marked  near 
the  center  by  an  impression  for 
the  insertion  of  the  Piriformis. 
The  inferior  border  corresponds 
to  the  line  of  junction  of  the 
base  of  the  trochanter  with  the 
lateral  surface  of  the  body;  it  is 
marked  by  a  rough,  prominent, 
slightly  curved  ridge,  which  gives 
origin  to  the  upper  part  of  the 
Vastus  lateralis.  The  anterior 
border  is  prominent  and  some- 
what irregular;  it  affords  inser- 
tion at  its  lateral  part  to  the 
Glutseus  minimus.  The  posterior 
border  is  very  prominent  and 
apipears  as  a  free,  rounded  edge, 
which  bounds  the  back  part  of 
the  trochanteric  fossa. 

The  Lesser  Trochanter  (tro- 
chanter minor;  small  trochanter) 
is  a  conical  eminence,  which 
varies  in  size  in  different  sub- 
jects; it  projects  from  the  lower 
and  back  part  of  the  base  of  the 
nuck.  From  its  apex  three  well- 
narked  borders  extend;  two  of 
these  are  above — a  medial  con- 
tinuous with  the  lower  border 
o'  the  neck,  a  lateral  with  the 
intertrochanteric  crest;  the  in- 
ferior border  is  continuous  with 
tlie  middle  division  of  the  linea 
aipera.    The  summit  of  the  tro- 

Piianter  is  rough,  and  gives  in- 
ortion    to   the   tendon  of  the 
Psoas  major. 

A  prominence,  of  variable  size, 
occurs  at  the  junction  of  the 
upper  part  of  the  neck  with  the 
greater  trochanter,  and  is  called 
tie  tubercle  of  the  femur;  it  is 
tie  point  of  meeting  of  five 
nmscles:  the  Gluta^us  minimus 
laterally,  the  Vastus  lateralis 
below,  and  the  tendon  of  the 
Obturator  internus  and  two 
Cremelli  above.  Running  ob- 
liquely downward  and  medial- 
ward  from  the  tubercle  is  the 
intertrochanteric  line  (spiral  line 
of  the  femur) ;  it  winds  around 
the  medial  side  of  the  body  of 
he  bone,  below  the  lesser  tro- 


THE  FEMUR 


Articular 
capsule 


Latenil 
epicondyle 

Groove  for 
tendon  of 
Popliteus 


I 


FiQ.  245 


Articular 
capsule 
Right  femur. 


Posterior  surface. 


i 


246  ^^^^^^  OSTEOLOGY 


chanter,  and  ends  about  5  cm.  below  this  eminence  in  the  linea  aspera.  Its  upper 
half  is  rough,  and  affords  attachment  to  the  iliofemoral  ligament  of  the  hip-joint; 
its  lower  half  is  less  prominent,  and  gives  origin  to  the  upper  part  of  the  Vastus 
medialis.  Running  obliquely  downward  and  medialward  from  the  summit  of  the 
greater  trochanter  on  the  posterior  surface  of  the  neck  is  a  prominent  ridge,  the 
intertrochanteric  crest.  Its  upper  half  forms  the  posterior  border  of  the  greater  tro- 
chanter, and  its  lower  half  runs  downward  and  medialward  to  the  lesser  trochanter. 
A  slight  ridge  is  sometimes  seen  commencing  about  the  middle  of  the  intertrochan- 
teric crest,  and  reaching  vertically  downward  for  about  5  cm.  along  the  back  part 
of  the  body:  it  is  called  the  linea  quadrata,  and  gives  attachment  to  the  Quad- 
ratus  femoris  and  a  few  fibers  of  the  Adductor  magnus.  Generally  there  is  merely 
a  slight  thickening  about  the  middle  of  the  intertrochanteric  crest,  marking  the 
attachment  of  the  upper  part  of  the  Quadratus  femoris. 

The  Body  or  Shaft  (corpus  femoris). — The  body,  almost  cylindrical  in  form,  is 
a  little  broader  above  than  in  the  center,  broadest  and  somewhat  flattened  from 
before  backward  below.  It  is  slightly  arched,  so  as  to  be  convex  in  front,  and  con- 
cave behind,  where  it  is  strengthened  by  a  prominent  longitudinal  ridge,  the  linea 
aspera.  It  presents  for  examination  three  borders,  separating  three  surfaces.  Of 
the  borders,  one,  the  linea  aspera,  is  posterior,  one  is  medial,  and  the  other,  lateral. 

The  linea  aspera  (Fig.  245)  is  a  prominent  longitudinal  ridge  or  crest,  on  the 
middle  third  of  the  bone,  presenting  a  medial  and  a  lateral  lip,  and  a  narrow 
rough,  intermediate  line.  Above,  the  linea  aspera  is  prolonged  by  three  ridges. 
The  lateral  ridge  is  very  rough,  and  runs  almost  vertically  upward  to  the  base  of 
the  greater  trochanter.  It  is  termed  the  gluteal  tuberosity,  and  gives  attachment 
to  part  of  the  Glutseus  maximus :  its  upper  part  is  often  elongated  into  a  roughened 
crest,  on  which  a  more  or  less  well-marked,  rounded  tubercle,  the  third  trochanter, 
is  occasionally  developed.  The  intermediate  ridge  or  pectineal  line  is  continued 
to  the  base  of  the  lesser  trochanter  and  gives  attachment  to  the  Pectineus;  the 
medial  ridge  is  lost  in  the  intertrochanteric  line;  between  these  two  a  portion  of  the 
Iliacus  is  inserted.  Below,  the  linea  aspera  is  prolonged  into  two  ridges,  enclosing 
between  them  a  triangular  area,  the  popliteal  surface,  upon  which  the  popliteal 
artery  rests.  Of  these  two  ridges,  the  lateral  is  the  more  prominent,  and  descends 
to  the  summit  of  the  lateral  condyle.  The  medial  is  less  marked,  especially  at  its 
upper  part,  where  it  is  crossed  by  the  femoral  artery.  It  ends  below  at  the  summit 
of  the  medial  condyle,  in  a  small  tubercle,  the  adductor  tubercle,  which  affords 
insertion  to  the  tendon  of  the  Adductor  magnus. 

From  the  medial  lip  of  the  linea  aspera  and  its  prolongations  above  and  below, 
the  Vastus  medialis  arises;  and  from  the  lateral  lip  and  its  upward  prolongation, 
the  Vastus  lateralis  takes  origin.  The  Adductor  magnus  is  inserted  into  the  linea 
aspera,  and  to  its  lateral  prolongation  above,  and  its  medial  prolongation  below. 
Between  the  Vastus  lateralis  and  the  Adductor  magnus  two  muscles  are  attached 
— viz.,  the  Glutseus  maximus  inserted  above,  and  the  short  head  of  the  Biceps 
femoris  arising  below.  Betweeen  the  Adductor  magnus  and  the  Vastus  medialis 
four  muscles  are  inserted:  the  Iliacus  and  Pectineus  above;  the  Adductor  brevis 
and  Adductor  longus  below.  The  linea  aspera  is  perforated  a  Uttle  below  its  center 
by  the  nutrient  canal,  which  is  directed  obliquely  upward. 

The  other  two  borders  of  the  femur  are  only  slightly  marked:  the  lateral  border 
extends  from  the  antero-inferior  angle  of  the  greater  trochanter  to  the  anterior 
extremity  of  the  lateral  condyle ;  the  medial  border  from  the  intertrochanteric  line, 
at  a  point  opposite  the  lesser  trochanter,  to  the  anterior  extremity  of  the  medial 
condyle. 

The  anterior  surface  includes  that  portion  of  the  shaft  which  is  situated  between 
the  lateral  and  medial  borders.  It  is  smooth,  convex,  broader  above  and  below 
than  in  the  center.  From  the  upper  three-fourths  of  this  surface  the  Vastus  inter- 
medius  arises;  the  lower  fourth  is  separated  from  the  muscle  by  the  intervention 


■THE  FEMUR 


247" 


of  the  synovial  membrane  of  the  knee-joint  and  a  bursa;  from  the  upper  part  of  it 
the  Articularis  genu  takes  origin.  The  lateral  surface  includes  the  portion  between 
the  lateral  border  and  the  linea  aspera;  it  is  continuous  above  with  the  correspond- 
ing surface  of  the  greater  trochanter,  below  with  that  of  the  lateral  condyle :  from 
its  upper  three-fourths  the  ^''astus  intermedins  takes  origin.  The  medial  surface 
includes  the  portion  between  the  medial  border  and  the  linea  aspera ;  it  is  continu- 
ous above  with  the  lower  border  of  the  neck,  below  with  the  medial  side  of  the 
medial  condyle:  it  is  covered  by  the  Vastus  medialis. 

The  Lower  Extremity  (distal  extremity) ,  (Fig.  246) . — The  lower  extremity,  larger 
than  the  upper,  is  somewhat  cuboid  in  form,  but  its  transverse  diameter  is  greater 
than  its  antero-posterior;  it  consists  of  two  oblong  eminences  known  as  the  condyles. 
In  front,  the  condyles  are  but  slightly  prominent,  and  are  separated  from  one  another 
by  a  smooth  shallow  articular  depression  called  the  patellar  surface;  behind,  they 
project  considerably,  and  the  interval  between  them  forms  a  deep  notch,  the 
intercondyloid  fossa.  The  lateral  condyle  is  the  more  prominent  and  is  the  broader 
both  in  its  antero-posterior  and  transverse  diameters,  the  medial  condyle  is  the 
longer  and,  when  the  femur  is  held  with  its  body  perpendicular,  projects  to  a  lower 


Laieral  groove 
Lateral  epicondyle 


Medial  groove 


Medial  epicondyle 
Semilunar  area 


Fio.  246. — Lower  extremity  of  right  femur  viewed  from  below. 

level.  When,  however,  the  femur  is  in  its  natural  oblique  position  the  lower  sur- 
faces of  the  two  condyles  lie  practically  in  the  same  horizontal  plane.  The  condyles 
ire  not  quite  parallel  with  one  another;  the  long  axis  of  the  lateral  is  almost 
directly  antero-posterior,  but  that  of  the  medial  runs  backward  and  medialward. 

P Their  opposed  surfaces  are  small,  rough,  and  concave,  and  form  the  walls  of  the 
intercondyloid  fossa.  This  fossa  is  limited  above  by  a  ridge,  the  intercondyloid 
line,  and  below  by  the  central  part  of  the  posterior  margin  of  the  patellar  surface. 
The  posterior  cruciate  ligament  of  the  knee-joint  is  attached  to  the  lower  and  front 
^^  part  of  the  medial  wall  of  the  fossa  and  the  anterior  cruciate  ligament  to  an  impres- 
^m  sion  on  the  upper  and  back  part  of  its  lateral  wall.  Each  condyle  is  surmounted 
by  an  elevation,  the  epicondyle.  The  medial  epicondyle  is  a  large  convex  eminence 
to  which  the  tibial  collateral  ligament  of  the  knee-joint  is  attached.  At  its  upper 
part  is  the  adductor  tubercle,  already  referred  to,  and  behind  it  is  a  rough  impres- 
sion which  gives  origin  to  the  medial  head  of  the  Gastrocnemius.  The  lateral 
epicondyle,  smaller  and  less  prominent  than  the  medial,  gives  attachment  to  the 
fibular  collateral  ligament  of  the  knee-joint.  Directly  below  it  is  a  small  depression 
from  which  a  smooth  well-marked  groove  curves  obliquely  upward  and  backward 
to  the  posterior  extremity  of  the  condyle.  This  groove  is  separated  from  the 
articular  surface  of  the  condyle  by  a  prominent  lip  across  which  a  second,  shallower 
groove  runs  vertically  downward  from  the  depression.  In  the  fresh  state  these 
grooves  are  covered  with  cartilage.  The  Popliteus  arises  from  the  depression; 
its  tendon  lies  in  the  oblique  groove  when  the  knee  is  flexed  and  in  the  vertical 


I 


248  ^        OSTEOLOGY 


h 


groove  when  the  knee  is  extended.  Above  and  behind  the  lateral  epieondyle  is 
an  area  for  the  origin  of  the  lateral  head  of  the  Gastrocnemius,  above  and  to  the 
medial  side  of  which  the  Plantaris  arises. 

The  articular  surface  of  the  lower  end  of  the  femur  occupies  the  anterior,  inferior, 
and  posterior  surfaces  of  the  condyles.  Its  front  part  is  named  the  patellar  surface 
and  articulates  with  the  patella;  it  presents  a  median  groove  which  extends  down- 
ward to  the  intercondyloid  fossa  and  two  convexities,  the  lateral  of  which  is  broader, 
more  prominent,  and  extends  farther  upward  than  the  medial.  The  lower  and 
posterior  parts  of  the  articular  surface  constitute  the  tibial  surfaces  for  articulation 
with  the  corresponding  condyles  of  the  tibia  and  menisci.  These  surfaces  are 
separated  from  one  another  by  the  intercondyloid  fossa  and  from  the  patellar 
surface  by  faint  grooves  which  extend  obliquely  across  the  condyles.  The  lateral 
groove  is  the  better  marked ;  it  runs  lateralward  and  forward  from  the  front  part 
of  the  intercondyloid  fossa,  and  expands  to  form  a  triangular  depression.  When 
the  knee-joint  is  fully  extended,  the  triangular  depression  rests  upon  the  anterior 
portion  of  the  lateral  meniscus,  and  the  medial  part  of  the  groove  comes  into  con- 
tact with  the  medial  margin  of  the  lateral  articular  surface  of  the  tibia  in  front 
of  the  lateral  tubercle  of  the  tibial  intercondyloid  eminence.  The  medial  groove 
is  less  distinct  than  the  lateral.  It  does  not  reach  as  far  as  the  intercondyloid 
fossa  and  therefore  exists  only  on  the  medial  part  of  the  condyle;  it  receives  the 
anterior  edge  of  the  medial  meniscus  when  the  knee-joint  is  extended.  Where  the 
groove  ceases  laterally  the  patellar  surface  is  seen  to  be  continued  backward  as 
a  semilunar  area  close  to  the  anterior  part  of  the  intercondyloid  fossa;  this  semi- 
lunar area  articulates  with  the  medial  vertical  facet  of  the  patella  in  forced  flexion 
of  the  knee-joint.  The  tibial  surfaces  of  the  condyles  are  convex  from  side  to  side 
and  from  before  backward.  Each  presents  a  double  curve,  its  posterior  segment 
being  an  arc  of  a  circle,  its  anterior,  part  of  a  cycloid.^ 

The  Architecture  of  the  Femur. — Koch'^  by  mathematical  analysis  has  "shown  that  in  every 
part  of  the  femur  there  is  a  remarkable  adaptation  of  the  inner  structure  of  the  bone  to  the  machan- 
ical  requirements  due  to  the  load  on  the  femur-head.  The  various  parts  of  the  femur  taken 
together  form  a  single  mechanical  structure  wonderfully  well-adapted  for  the  efficient,  economical 
transmission  of  the  loads  from  the  acetabulum  to  the  tibia;  a  structure  in  which  every  element 
contributes  its  modicum  of  strength  in  the  manner  required  by  theoretical  mechanics  for  maximum 
efficiency."  "The  internal  structure  is  everywhere  so  formed  as  to  provide  in  an  efficient  manner 
for  all  the  internal  stresses  which  occur  due  to  the  load  on  the  femur-head.  Throughout  the  femur, 
with  the  load  on  the  femur-head,  the  bony  material  is  arranged  in  the  paths  of  the  maximum 
internal  stresses,  which  are  thereby  resisted  with  the  greatest  efficiency,  and  hence  with  maximum 
economy  of  material."  "The  conclusion  is  inevitable  that  the  inner  structure  and  outer  form  of 
the  femur  are  governed  by  the  conditions  of  maximum  stress  to  which  the  bone  is  subjected 
normally  by  the  preponderant  load  on  the  femur- head;  that  is,  by  the  body  weight  transmitted 
to  the  femur-head  through  the  acetabulum."  "The  femur  obeys  the  mechanical  laws  that  govern 
other  elastic  bodies  under  stress ;  the  relation  between  the  computed  internal  stresses  due  to  the 
load  on  the  femur-head,  and  the  internal  structure  of  the  different  portions  of  the  femur  is  in  very 
close  agreement  with  the  theoretical  relations  that  should  exist  between  stress  and  structure  for 
maximum  economy  and  efficiency;  and,  therefore,  it  is  believed  that  the  following  laws  of  bone 
structure  have  been  demonstrated  for  the  femur: 

"1.  The  inner  structure  and  external  form  of  human  bone  are  closely  adapted  to  the  mechanical 
conditions  existing  at  every  point  in  the  bone. 

"2.  The  inner  architecture  of  normal  bone  is  determined  by  definite  and  exact  requirements  of 
mathematical  and  mechanical  laws  to  produce  a  maximum  of  strength  with  a  minimum  of 
material." 

The  Inner  Architecture  of  the  Upper  Femur. — "The  spongy  bone  of  the  upper  femur  (to  the 
lower  limit  of  the  lesser  trochanter)  is  composed  of  two  distinct  systems  of  trabeculae  arranged  in 
curved  paths:  one,  which  has  its  origin  in  the  medial  (inner)  side  of  the  shaft  and  curving  upward 

'  A  cycloid  is  a  curve  traced  by  a  point  in  the  circumference  of  a  wheel  when  the  wheel  is  rolled  along  in  a  straight 
line. 

»  The  Laws  of  Bone  .\rchitecture.  Am.  Jour,  of  Anat.,  21,  1917.  The  following  paragraphs  are  taken  almost  ver- 
batum  from  Koch's  article  in  which  we  have  the  first  correct  mathematical  analysis  of  the  femur  in  support  of  the 
theory  of  the  functional  form  of  bone  proposed  by  Wolff  and  also  by  Rous. 


THE  FEMUR 


249 


in  a  fan-like  radiation  to  the  opposite  side  of  the  bone;  the  other,  having  origin  in  the  lateral 
(outer)  portion  of  the  shaft  and  arching  upward  and  medially  to  end  in  the  upper  surface  of  the 
greater  trochanter,  neck  and  head.    These  two  systems  intersect  each  other  at  right  angles. 

"A.  Medial  (Compressive)  System  of  Traheculce. — As  the  compact  bone  of  the  medial  (inner) 
part  of  the  shaft  nears  the  head  of  the  femur  it  gradually  becomes  thinner  and  finally  reaches  the 
articular  surface  of  the  head  as  a  very  thin  layer.    From  a  point  at  about  the  lower  level  of  the 


Fig.  247. — Frontal  longitudinal  midsection  of  upper  femur. 


lesser  trochanter,  2|  to  3  inches  from  the  lower  limit  of  the  articular  surface  of  the  head,  the 
Irabecula;  branch  off  from  the  shaft  in  smooth  curves,  spreading  radially  to  cross  to  the  opposite 
.-ide  in  two  well-defined  groups:  a  lower,  or  secondary  group,  and  an  upper,  or  principal  group. 

"a.  The  Secondary  Compressive  Group. — This  group  of  trabecular  leaves  the  inner  border  of  the 
shaft  beginning  at  about  the  level  of  the  lesser  trochanter,  and  for  a  distance  of  almost  2  inches 
along  the  curving  shaft,  with  which  the  separate  trabecular  make  an  angle  of  about  15  degrees. 


■ 


OSTEOLOGY 


II 


They  curve  outwardly  and  upwardly  to  cross  in  radiating  smooth  curves  to  the  opposite  side. 
The  lower  filaments  end  in  the  region  of  the  greater  trochanter:  the  adjacent  filaments  above 
these  pursue  a  more  nearly  vertical  course  and  end  in  the  upper  portion  of  the  neck  of  the  femur. 
The  trabeculae  of  this  group  are  thin  and  with  wide  spaces  between  them.  As  they  traverse 
the  space  between  the  medial  and  lateral  surfaces  of  the  bone  they  cross  at  right  angles  the  system 
of  curved  trabeculae  which  arise  from  the  lateral  (outer)  portion  of  the  shaft.  (Figs.  247  and  249.) 
"b.  The  Principal  Compressive  Group. — This  group  of  trabeculae  (l^igs.  247  and  249)  springs 
from  the  medial  portion  of  the  shaft  just  above  the  group  above-described,  and  spreads  upward 
and  in  slightly  radial  smooth  curved  lines  to  reach  the  upper  portion  of  the  articular  surface  of 
the  head  of  the  femur.  These  trabeculse  are  placed  very  closely  together  and  are  the  thickest  ones 
seen  in  the  upper  femur.  They  are  a  prolongation  of  the  shaft  from  which  they  spring  in  straight 


LOAD 


n 


Fig.  248. — Diagram  of  the  lines  of  stress  in  the  upper  femur,  based  upon  the  mathematical  analysis  of  the  right 
femur.  These  result  from  the  combination  of  the  different  kinds  of  stres.ses  at  each  point  in  the  femur.  (After 
Koch.) 

lines  which  gradually  curve  to  meet  at  right-angles  the  articular  surface.  There  is  no  change  as 
they  cross  the  epiphyseal  line.  They  also  intersect  at  right-angles  the  system  of  lines  which  rise 
from  the  lateral  side  of  the  femur. 

"This  system  of  principal  and  secondary  compressive  trabeculae  corresponds  in  position  and  in 
curvature  with  the  lines  of  maximum  compressive  stress,  which  were  traced  out  in  the  mathematical 
analysis  of  this  portion  of  the  femur.     (Figs.  247  and  250.) 

"B.  Lateral  (Tensile)  System  of  Traheculce. — As  the  compact  bone  of  the  outer  portion  of  the 
shaft  approaches  the  greater  trochanter  it  gradually  decreases  in  thickness.  Beginning  at  a  point 
about  1  inch  below  the  level  of  the  lower  border  of  the  greater  trochanter,  numerous  thin  trabeculae 
are  given  off  from  the  outer  portion  of  the  shaft.     These  trabeculae  lie  in  three  distinct  groups. 

"c.  The  Greater  Trochanter  Group. — These  trabeculae  rise  from  the  outer  part  of  the  shaft  just 
below  the  greater  trochanter  and  rise  in  thin,  curving  lines  to  cross  the  region  of  the  greater 
trochanter  and  end  in  its  upper  surface.    Some  of  these  filaments  are  poorly  defined.    This  group 


THE  FEMUR 


251 


I 


Fig.  249. — Frontal  longitudinal  midsection  of  left 
;mur.  Taken  from  the  same  subject  as  the  one  that 
■as  analyzed  and  shown  in  Figs.  248  and  250.  4  of 
atural  size.     (After  Koch.) 


Fig.  250.  —  Diagram  of  the  computed  lines  of 
maximum  stress  in  the  normal  femur.  The  section 
numbers  2,  4,  6,  8,  etc.,  show  the  positions  of  the 
transverse  sections  analyzed.  The  amounts  of  the 
maximum  tensile  and  compressive  stress  at  the 
various  sections  are  given  for  a  load  of  100  pounds  on 
the  femur-head.  For  the  standing  position  ("at  at- 
tention") these  stresses  are  multiplied  by  0.6,  for 
walking  by  1.6  and  for  running  by  3.2.     (After  Koch.) 


OSTEOLOGY 


The  trabecule  of  this 


intersects  the  trabeculse  of  group  (o)  which  rise  from  the  opposite  side, 
group  evidently  carry  small  stresses,  as  is  shown  by  their  slenderness. 

"d.  The  Principal  Tensile  Group. — This  group  springs  from  the  outer  part  of  the  shaft  imme- 
diately below  group  c,  and  curves  convexly  upward  and  inward  in  nearly  parallel  lines  across  1  he 
neck  of  the  femur  and  ends  in  the  inferior  portion  of  the  head.  These  trabeculse  are  somewhat 
thinner  and  more  widely  spaced  than  those  of  the  principal  compressive  group  (6).  All  the  trabec- 
ular of  this  group  cross  those  of  groups  (a)  and  (6)  at  right  angles.  This  group  is  the  most  impor- 
tant of  the  lateral  system  (tensile)  and,  as  will  be  shown  later,  the  greatest  tensile  stresses  of  the 
upper  femur  are  carried  by  the  trabecular  of  this  group. 

"e.  The  Secondary  Tensile  Group. — This  group  consists  of  the  trabeculse  which  spring  from  the 
outer  side  of  the  shaft  and  lie  below  those  of  the  preceding  group.  They  curve  upward  and  medially 
across  the  axis  of  the  femur  and  end  more  or  less  irregularly  after  crossing  the  midline,  but  a 
number  of  these  filaments  end  in  the  medial  portion  of  the  shaft  and  neck.  They  cross  at  right 
angles  the  trabeculse  of  group  (a). 


FiQ.  251.- 


0  =  C0MPRESS10N 
•  =  TENSION 
C=COMP.  &  TENSION 
NEUTRAL  AXIS 


-Intensity  of  the  maximum  tensile  and  compressive  stresses  in  the  upper  femur.    Computed  for  the  loatl  of 
100  pounds  on  the  right  femur.     Corresponds  to  the  upper  part  of  Fig.  250.     (After  Koch.) 


"In  general,  the  trabeculse  of  the  tensile  system  are  lighter  in  structure  than  those  of  the  com- 
pressive system  in  corresponding  positions.  The  significance  of  the  difference  in  thickness  of  these 
two  systems  is  that  the  thickness  of  the  trabeculse  varies  with  the  intensity  of  the  stresses  at  any 
given  point.  Comparison  of  Fig.  247  with  Fig.  251  will  show  that  the  trabeculse  of  the  com- 
pressive system  carry  heavier  stresses  than  those  of  the  tensile  system  in  corresponding  positions. 
For  example,  the  maximum  tensile  stress  at  section  8  (Fig.  251)  in  the  outermost  fiber  is  771 
pounds  per  square  inch,  and  at  the  corresponding  point  on  the  compressive  side  the  compressive 
stress  is  954  pounds  per  square  inch.  Similar  comparisons  may  be  made  at  other  points,  which 
confirm  the  conclusion  that  the  thickness  and  closeness  of  spacing  of  the  trabeculse  varies  in 
proportion  to  the  intensity  of  the  stresses  carried  by  them. 

"It  will  be  seen  that  the  trabeculse  lie  exactly  in  the  paths  of  the  maximum  tensile  and  com- 
pressive stresses  (compare  Figs.  247,  248  and  251),  and  hence  these  trabeculse  carry  these  stresses 
in  the  most  economical  manner.  This  is  in  accordance  with  the  well-recognized  principle  of 
mechanics  that  the  most  direct  manner  of  transmitting  stress  is  in  the  direction  in  which  the  stress 
acts. 


THE  FEMUR 


253 


"Fig.  249  shows  a  longitudinal  frontal  section  through  the  left  femur,  which  is  the  mate  of  the 
right  femur  on  which  the  mathematical  analysis  was  made.  In  this  midsection  the  system  of 
tensile  trabeculse,  which  rises  from  the  lateral  (outer)  part  of  the  shaft  and  crosses  over  the  central 
area  to  end  in  the  medial  portion  of  the  shaft,  neck  and  head,  is  clearly  shown.  This  figure  also 
shows  the  compressive  system  of  trabeculse  which  rises  on  the  medial  portion  of  the  shaft  and 
crosses  the  central  area  to  end  in  the  head,  neck  and  greater  trochanter.  By  comparing  the  posi- 
lion  of  these  two  systems  of  trabecula?  shown  in  Fig.  249  with  the  lines  of  maximum  and  minimum 
stresses  sho^Ti  in  Figs.  248  and  2.50  it  is  seen  that  the  tensile  system  of  trabeculse  corresponds 
exactly  with  the  position  of  the  lines  of  maximum  and  minimum  tensile  stresses  which  were 
<letermined  by  mathematical  analysis.  In  a  similar  manner,  the  compressive  system  of  trabecular 
in  Fig.  249  corresponds  exactly  with  the  lines  of  maximum  and  minimum  compressive  stresses 
("omputed  by  mathematical  analysis. 

"The  amount  of  vertical  shear  varies  almost  uniformly  from  a  maximum  of  90  pounds  (90  per 
cent,  of  the  load  on  the  femur-head)  midway  between  sections  4  and  6,  to  a  minimum  of  — 5.7 
])ounds  at  section  18"  (Fig.  251).  There  is  a  gradual  diminution  of  the  spongy  bone  from  section 
()  to  section  18  parallel  with  the  diminished  intensities  of  the  vertical  shear. 

1.  The  trabeculse  of  the  upper  femur,  as  shown  in  frontal  sections,  are  arranged  in  two  general 
systems,  compressive  and  tensile,  which  correspond  in  position  with  the  lines  of  maximum  and 
minimum  stresses  in  the  femur  determined  by  the  mathematical  analysis  of  the  femur  as  a  mechan- 
ical structure. 

2.  The  thickness  and  spacing  of  the  trabeculse  vary  with  the  intensity  of  the  maximum  stresses 
at  various  points  in  the  upper  femur,  being  thickest  and  most  closely  spaced  in  the  regions  where 
the  greatest  stresses  occur. 

3.  The  amount  of  bony  material  in  the  spongy  bone  of  the  upper  femur  varies  in  proportion  to 
lhe  intensity  of  the  shearing  force  at  the  various  sections. 

4.  The  arrangement  of  the  trabeculse  in  the  positions  of  maximum  stresses  is  such  that  the 
greatest  strength  is  secured  with  a  minimum  of  material. 

Significance  of  the  Inner  Architecture  of  the  Shaft. — 1 .  Economy  for  resisting  shear.  The  shearing 
stresses  are  at  a  minimum  in  the  shaft.  "It  is  clear  that  a  minimum  amount  of  material  will  be 
lequired  to  resist  the  shearing  stresses."  As  horizontal  and  vertical  shearing  stresses  are  most 
efficiently  resisted  by  material  placed  near  the  neutral  plane,  in  this  region  a  minimum  amount 
i)f  material  will  be  needed  near  the  neutral  axis.  In  the  shaft  there  is  very  little  if  any  material 
in  the  central  space,  practically  the  only  material  near  the  neutral  plane  being  in  the  compact 
()one,  but  l>ing  at  a  distance  from  the  neutral  axis.    This  conforms  to  the  requirement  of  mechanics 

I  ■or  economy,  as  a  minimum  of  material  is  provided  for  resisting  shearing  stresses  where  these 

I  .stresses  are  a  minimum. 

2.  Economy  for  resisting  bending  moment.  "The  bending  moment  increases  from  a  minimum 
[.it  section  4  to  a  maximum  between  sections  16  and  18,  then  gradually  decreases  almost  uniformly 

X)  0  near  section  75."  "To  resist  bending  moment  stresses  most  effectively  the  material  should 
06  as  far  from  the  neutral  axis  as  possible."  It  is  evident  that  the  hollow  shaft  of  the  femur  is 
in  efficient  sti-ucture  for  resisting  bending  moment  stresses,  all  of  the  material  in  the  shaft  being 
•elatively  at  a  considerable  distance  from  the  neutral  axis.  It  is  evident  that  the  hollow  shaft 
jrovides  efficiently  for  resisting  bending  moment  not  only  due  to  the  load  on  the  femur-head,  but 
Tom  any  other  loads  tending  to  produce  bending  in  other  planes. 

3.  Economy  for  resisting  axial  stress. 

The  inner  architecture  of  the  shaft  is  adapted  to  resist  in  the  most  efficient  manner  the  com- 
oined  action  of  the  minimal  shearing  forces  and  the  axial  and  maximum  bending  stre.sses. 

The  structure  of  the  shaft  is  such  as  to  secure  great  strength  with  a  relatively  small  amount  of 
Jiaterial. 

The  Distal  Portion  of  the  Femur.— In  frontal  section  (Fig.  249)  in  the  distal  6  inches  of  the 
"emur  "there  are  to  be  seen  two  main  systems  of  trabeculse,  a  longitudinal  and  a  transverse 
[;jystem.  The  trabeculse  of  the  former  rise  from  the  inner  wall  of  the  shaft  and  continue  in  per- 
"ectly  straight  lines  parallel  to  the  axis  of  the  shaft  and  proceed  to  the  epiphyseal  line,  whence 
phey  continue  in  more  or  less  curved  lines  to  meet  the  articular  surface  of  the  knee-joint  at  right 
kiingles  at  every  point.  Near  the  center  there  are  a  few  thin,  delicate,  longitudinal  trabecula; 
rjehich  spring  from  the  longitudinal  trabeculse  just  described,  to  which  they  are  joined  by  fine 
jiiransverse  filaments  that  lie  in  planes  parallel  to  the  sagittal  plane. 

"The  trabeculse  of  the  transverse  sj'stem  are  somewhat  lighter  in  structure  than  those  of  the 
longitudinal  system,  and  consist  of  numerous  trabeculse  at  right  angles  to  the  lattef. 

"As  the  distal  end  of  the  femur  is  approached  the  shaft  gradually  becomes  thinner  until  the 

[iirticular  surface  is  reached,  where  there  remains  only  a  thin  shell  of  compact  bone.    With  the 

radual  thinning  of  the  compact  bone  of  the  shaft,  there  is  a  simultaneous  increase  in  the  amount 

[of  the  spongy  bone,  and  a  gradual  flaring  of  the  femur  which  gives  this  portion  of  the  bone  a 

radually  increasing  gross  area  of  cross-section. 

"There  is  a  marked  thickening  of  the  shell  of  bone  in  the  region  of  the  intercondyloid  fossa 
[where  the  anterior  and  posterior  crucial  ligaments  are  attached.     This  thickened  area  is  about 


254 


OSTEOLOGY 


Appears  at 
4:th  year  ; 
joins  body 

about  ISth  yr. 


Appears  at 
end  of  1st  yr.  ; 

joins  body 
about  ISth  yr. 

Appears  ISth-lith 
year  ;  joins  body 
about  18th  year 


Joins  body  at 
20th  year 


Appears  at 

9th  month  of 

fetal  life 

Lower  extremity 

Fig.  252. — Plan  of  ossification  of  the  femur. 
five  centers. 


From 


0.4  inch  iri  diameter  and  consists  of  compac 
bone  from  which  a  number  of  thick  trabeci  Uae'' 
pass  at  right  angles  to  the  main  longitudinal 
system.  The  inner  structure  of  the  bone  is  here 
evidently  adapted  to  the  efficient  distribution  of 
the  stresses  arising  from  this  ligamentary  at- 
tachment. 

"Near  the  distal  end  of  the  femur  the  longi- 
tudinal trabecular  gradually  assume  curved 
paths  and  end  perpendicularly  to  the  articular 
surface  at  every  point.  Such  a  structure  is  in 
accordance  with  the  principles  of  mechanics, 
as  stresses  can  be  communicated  througli  a 
frictionless  joint  only  in  a  direction  perpendic- 
ular to  the  joint  surface  at  every  point. 

"With  practically  no  increase  in  the  amount 
of  bony  material  used,  there  is  a  greatly  increased 
stability  produced  by  the  expansion  of  the  lower 
femur  from  a  hollow  shaft  of  compact  bone  to  a 
structure  of  much  larger  cross-section  almost 
entirely  composed  of  spongy  bone. 

"Significance  of  the  Inner  Architecture  of  the 
Distal  Part  of  the  Femur. — The  function  of  the 
lower  end  of  the  femur  is  to  transmit  through  a 
hinged  joint  the  loads  carried  by  the  femur.  For 
stability  the  width  of  the  bearing  on  which  the 
hinge  action  occurs  should  be  relatively  large. 
For  economy  of  material  the  expansion  of  the  end 
bearing  should  be  as  lightly  constructed  as  is 
consistent  with  proper  strength.  In  accordance 
with  the  principles  of  mechanics , 


Fig.  253. — Epiphysial  lines  of  femur  in  a  young 
adult.  Anterior  aspect.  The  lines  of  attachment  of 
the  articular  capsules  are  in  blue. 


Fig.  254. — Epiphysial  lines  of  femur  in  a  young  adult. 
Posterior  aspect.  The  lines  of  attachment  of  the  articular 
capsules  are  in  blue. 


THE  PATELLA 


255 


The  Patella  (Ejiee  Cap). 


the  most  efficient  manner  in  which  stresses  are  transmitted  is  by  the  arrangement  of  the  resist- 
ing material  in  lines  parallel  to  the  direction  in  which  the  stresses  occur  and  in  the  paths  taken 
b}'  the  stresses.  Theoretically  the  most  efficient  manner  to  attain  these  objects  would  be  to  pro- 
long the  innermost  filaments  of  the  bone  as  straight  lines  parallel  to  the  longitudinal  axis  of 
the  bone,  and  gradually  to  flare  the  outer  shell  of  compact  bone  outward,  and  continuing  to  give 
ofr  filaments  of  bone  parallel  to  the  longitudinal  axis  as  the  distal  end  of  the  femur  is  approached. 
Tliese  filaments  should  be  well-braced  transversely  and  each  should  carry  its  proportionate 
part  of  the  total  load,  parallel  to  the  longitudinal  axis,  transmitting  it  eventually  to  the 
articular  surface,  and  in  a  direction  perpendicular  to  that  surface." 

Referring  to  Fig.  249,  it  is  seen  that  the  large  expansion  of  the  bone  is  produced  by  the  gradual 
transition  of  the  hollow  shaft  of  compact  bone  to  cancellated  bone,  resulting  in  the  production 
of  a  much  larger  volume.  The  trabecular  are  given  off  from  the  shaft  in  lines  parallel  to  the 
longitudinal  axis,  and  are  braced  transversely  by  two  series  of  trabeculae  at  right  angles  to 
each  other,  in  the  same  manner  as  required  theoretically  for  economy. 

Although  the  action  of  the  muscles  exerts  an  appreciable  effect  on  the  stresses  in  the  femur, 
it  is  relatively  small  and  very  complex  to  analyze  and  has  not  been  considered  in  the  above  analj'sis. 

Ossification  (Figs.  252,  253,  254). — The  femur  is  ossified  from  jive  centers:  one  for  the  body, 
one  for  the  head,  one  for  each  trochanter,  and  one  for  the  lower  extremity.  Of  all  the  long  bones, 
except  the  clavicle,  it  is  the  first  to  show  traces  of  ossification;  this  commences  in  the  middle  of 
the  body,  at  about  the  seventh  week  of  fetal  life,  and  rapidly  extends  upw^frd  and  downward. 
The  centers  in  the  epiphyses  appear  in  the  following  order :  in  the  lower  end  of  the  bone,  at  the 
ninth  month  of  fetal  life  (from  this  center  the  condyles  and  epicondyles  are  formed) ;  in  the  head, 
at  the  end  of  the  first  year  after  birth;  in  the  greater  trochanter,  during  the  fourth  year;  and 
in  the  lesser  trochanter,  between  the  thirteenth  and  fourteenth  years.  The  order  in  which  the 
epiphyses  are  joined  to  the  body  is  the  reverse  of  that  of  their  appearance;  they  are  not  united 
uritil  after  puberty,  the  lesser  trochanter  being  first  joined,  then  the  greater,  then  the  head,  and, 
lastly,  the  inferior  extremity,  which  is  not  united  until  the  twentieth  year. 

The  patella  (Figs.  255,  25G)  is  a  flat,  triangular  bone,  situated  on  the  front  of 
tj  e  knee-joint.  It  is  usually  regarded  as  a  sesamoid  bone,  developed  in  the 
tendon  of  the  Quadriceps  femoris, 
and  resembles  these  bones  (1)  in 
b<ing  developed  in  a  tendon;  (2)  in 
iti  center  of  ossification  presenting 
a  knotty  or  tuberculated  outline; 
(3)  in  being  composed  mainly  of 
d<!nse  cancellous  tissue.  It  serves 
tc  protect  the  front  of  the  joint, 
and  increases  the  leverage  of  the 
Quadriceps  femoris  by  making  it 
a(t  at  a  greater  angle.  It  has  an 
anterior  and  a  posterior  surface 
three  borders,  and  an  apex. 

Surfaces. — ^The  anterior  surface  is  convex,  perforated  by  small  apertures  for  the 
p;,ssage  of  nutrient  vessels,  and  marked  by  numerous  rough,  longitudinal  striae. 
T  lis  surface  is  covered,  in  the  recent  state,  by  an  expansion  from  the  tendon  of 
the  Quadriceps  femoris,  which  is  continuous  below  with  the  superficial  fibers  of 
the  ligamentum  patelLne.  '  It  is  separated  from  the  integument  by  a  bursa.  The 
posterior  surface  presents  above  a  smooth,  oval,  articular  area,  divided  into  two 
facets  by  a  vertical  ridge;  the  ridge  corresponds  to  the  groove  on  the  patellar 
surface  of  the  femur,  and  the  facets  to  the  medial  and  lateral  parts  of  the  same 
surface;  the  lateral  facet  is  the  broader  and  deeper.  Below  the  articular  surface 
is  a  rough,  convex,  non-articular  area,  the  lower  half  of  which  gives  attachment 
to  the  ligamentum  patellae;  the  upper  half  is  separated  from  the  head  of  the  tibia 
by  adipose  tissue. 

Borders. — The  base  or  superior  border  is  thick,  and  sloped  from  behind,  down- 
ward, and  forward :  it  gives  attachment  to  that  portion  of  the  Quadriceps  femoris 


Fia.  255.— Right  patella. 
Anterior  surface. 


Fig.  256.— Right  patella. 
Posterior  surface. 


256 


I 


which  is  derived  from  the  Rectus  femoris  and  Vastus  intermedius.  The  medial  and 
lateral  borders  are  thinner  and  converge  below:  they  give  attachment  to  tliose 
portions  of  the  Quadriceps  femoris  which  are  derived  from  the  Vasti  laterahs  and 
mediahs. 

Apex. — The  apex  is  pointed,  and  gives  attachment  to  the  hgaraentum  patellae. 

Structure. — The  patella  consists  of  a  nearly  uniform  dense  cancellous  tissue,  covered  by  a 
thin  compact  lamina.  The  cancelli  immediately  beneath  the  anterior  surface  are  arranged 
parallel  with  it.  In  the  rest  of  the  bone  they  radiate  from  the  articular  surface  toward  the  other 
parts  of  the  bone. 

Ossification. — The  patella  is  ossified  from  a  single  center,  which  usually  makes  its  appearance 
in  the  second  or  third  year,  but  may  be  delayed  until  the  sixth  year.  More  rarely,  the  bone  is 
developed  by  two  centers,  placed  side  by  side.    Ossification  is  completed  about  the  age  of  puberty. 

Articulation. — The  patella  articulates  with  the  femur. 


Tuberosity 


feral 

di/Ze 


Inter  condyloid  eminence. 

Fig.  257. — Upper  surface  of  right  tibia. 


The  Tibia  (Shin  Bone). 

The  tibia   (Figs.   258,   259)   is  situated   at    the  medial   side  of  the  leg,  and, 
excepting  the  femur,  is  the  longest  bone  of  the  skeleton.    It  is  prismoid  in  form, 

expanded  above,  where  it  enters  into  the 
knee-joint,  contracted  in  the  lower  third, 
and  again  enlarged  but  to  a  lesser  extent 
below.  In  the  male,  its  direction  is  vertical, 
and  parallel  with  the  bone  of  the  opposite 
side;  but  in  the  female  it  has  a  slightly 
oblique  direction  downward  and  lateralward, 
to  compensate  for  the  greater  obliquity  of 
the  femur.  It  has  a  body  and  two  extremities. 
The  Upper  Extremity  {proximal  extremity). 
— The  upper  extremity  is  large,  and  expanded 
into  two  eminences,  the  medial  and  lateral 
condyles.  The  superior  articular  surface  pre- 
sents two  smooth  articular  facets  (Fig.  257). 
The  medial  facet,  oval  in  shape,  is  slightly 
concave  from  side  to  side,  and  from  before 
backward.  The  lateral,  nearly  circular,  is 
concave  from  side  to  side,  but  slightly  convex  from  before  backward,  especially 
at  its  posterior  part,  where  it  is  prolonged  on  to  the  posterior  surface  for  a 
short  distance.  The  central  portions  of  these  facets  articulate  with  the  con- 
dyles of  the  femur,  while  their  peripheral  portions  support  the  menisci  of  the 
knee-joint,  which  here  intervene  between  the  two  bones.  Between  the  artic- 
ular facets,  but  nearer  the  posterior  .than  the  anterior  aspect  of  the  bone,  is  the 
intercondyloid  eminence  {spine  of  tibia),  surmounted  on  either  side  by  a  prominent 
tubercle,  on  to  the  sides  of  which  the  articular  facets  are  prolonged;  in  front  of 
and  behind  the  intercondyloid  eminence  are  rough  depressions  for  the  attachment 
of  the  anterior  and  posterior  cruciate  ligaments  and  the  menisci.  The  anterior 
surfaces  of  the  condyles  are  continuous  with  one  another,  forming  a  large  somewhat 
flattened  area;  this  area  is  triangular,  broad  above,  and  perforated  by  large  vascular 
foramina;  narrow  below  where  it  ends  in  a  large  oblong  elevation,  the  tuberosity  of 
the  tibia,  which  gives  attachment  to  the  ligamentum  patellae;  a  bursa  intervenes 
between  the  deep  surface  of  the  ligament  and  the  part  of  the  bone  immediately 
above  the  tuberosity.  Posteriorly,  the  condyles  are  separated  from  each  other  by 
a  shallow  depression,  the  posterior  intercondyloid  fossa,  which  gives  attachment  to 
part  of  the  posterior  cruciate  ligament  of  the  knee-joint.  The  medial  condyle 
presents  posteriorly  a  deep  transverse  groove,  for  the  insertion  of  the  tendon  of 


THE  TIBIA 


25i 


I 


the  Semimembranosus.  Its  medial 
s^urface  is  convex,  rough,  and  promi- 
nent; it  gives  attachment  to  the 
tibial  collateral  ligament.  The  lat- 
eral condyle  presents  posteriorly  a 
flat  articular  facet,  nearly  circular 
in  form,  directed  downward,  back- 
ward, and  lateral  ward,  for  articu- 
lation with  the  head  of  the  fibula. 
Its  lateral  surface  is  convex,  rough, 
and  prominent  in  front:  on  it  is 
an  eminence,  situated  on  a  level 
with  the  upper  border  of  the  tuber- 
osity and  at  the  junction  of  its 
anterior  and  lateral  surfaces,  for 
the  attachment  of  the  iliotibial 
band.  Just  below  this  a  part  of 
the  Extensor  digitorum  longus 
takes  origin  and  a  slip  from  the 
tendon  of  the  Biceps  femoris  is 
inserted. 

The  Body  or  Shaft  {coryiLS  tibiw). 
— The  body  has  three  borders  and 
three  surfaces. 

Borders. — The  anterior  crest  or 
border,  the  most  prominent  of  the 
three,  commences  above  at  the 
tuberosity,  and  ends  below  at  the 
anterior  margin  of  the  medial 
jnalleolus.  It  is  sinuous  and 
j)rominent  in  the  upper  two-thirds 
of  its  extent,  but  smooth  and 
]«unded  below;  it  gives  attach- 
]tient  to  the  deep  fascia  of  the  leg. 

The  medial  border  is  smooth  and 
K)unded  above  and  below,  but 
more  prominent  in  the  center;  it 
begins  at  the  back  part  of  the 
medial  condyle,  and  ends  at  the 
posterior  border  of  the  medial 
malleolus;  its  upper  part  gives 
attachment  to  the  tibial  collat- 
eral ligament  of  the  knee-joint 
to  the  extent  of  about  5  cm., 
and  insertion  to  some  fibers  of 
the  Popliteus;  from  its  middle 
|hird  some  fibers  of  the  Soleus 
and  Flexor  digitorum  longus  take 
origin. 

The  interosseous  crest  or  lateral 

fider  is  thin  and  prominent,  espe- 
lially  its  central  part,  and  gives  at- 

chment  to  the  interosseous  mem- 
rane;  it  commences  above  in  front 
f  the  fibular  articular  facet,  and 
17 


Articular  capsule 


Styloid  process ' 

Fibular 
collateral' 
ligament 


'  condyle 


■^eat' 


JcVo* 


'Mis     "I"!'. 


/ 


v; 


8    "^ 


Articular 
capsule 


ttredi,.  jt. 


H-\ 


'.t~-t^5 


Lateral  malleolus 
Fig.  258. — Bones  of  the  right  leg. 


Medial  malleolus 


Anterior  surface. 


258 


OSTEOLOGY 


femur 


Articidar 
capsule 


Articular 
capsule 

Styloid 
process 


bifurcates  below,  to  form  the  boundaries  of  a  triangular  rough  surface,  for  the 
attachment  of  the  interosseous  ligament  connecting  the  tibia  and  fibula. 

Surfaces. — The  medial  surface 
is  smooth,  convex,  and  broader 
above  than  below;  its  up})er 
third,  directed  forward  and 
medial  ward,  is  covered  by  the 
aponeurosis  derived  from  the 
tendon  of  the  Sartorius,  and  by 
the  tendons  of  the  Gracilis  and 
Semitendinosus,  all  of  which 
are  inserted  nearly  as  far  for- 
ward as  the  anterior  crest;  in 
the  rest  of  its  extent  it  is  sub- 
cutaneous. 

The  lateral  surface  is  narrower 
than  the  medial ;  its  upper  tw  o- 
thirds  present  a  shallow  groove 
for  the  origin  of  the  Tibialis 
anterior;  its  lower  third  is 
smooth,  convex,  curves  grad- 
ually forward  to  the  anterior 
aspect  of  the  bone,  and  is 
covered  by  the  tendons  of  the 
Tibialis  anterior,  Extensor  hal- 
lucis  longus,  and  Extensor  digi- 
torum  longus,  arranged  in  this 
order  from  the  medial  side. 

The  posterior  surface  (Fig.  259) 
presents,  at  its  upper  part,  a 
prominent  ridge,  the  popliteal 
line,  which  extends  obliquely 
downward  from  the  back  part  of 
the  articular  facet  for  the  fibula 
to  the  medial  border,  at  the 
junction  of  its  upper  and  middle 
thirds;  it  marks  the  lower  limit 
of  the  insertion  of  the  Popliteus, 
serves  for  the  attachment  of  the 
fascia  covering  this  muscle,  and 
gives  origin  to  part  of  the 
Soleus,  Flexor  digitorum  longus, 
and  Tibialis  posterior.  The 
triangular  area,  above  this  line, 
gives  insertion  to  the  Popliteus. 
The  middle  third  of  the  poste- 
rior surface  is  divided  by  a  ver- 
tical ridge  into  two  parts;  the 
ridge  begins  at  the  popliteal  line 
and  is  well-marked  above,  but 
indistinct  below;  the  medial  and 
broader  portion  gives  origin  to 
the  Flexor  digitorum  longus, 
.  ,.    ,  ,         ,  the  lateral  and  narrower  to  part 

Articular  capsule  T'-u*    r  +     •  T'U 

259.— Bones  of  the  right  leg.     Posterior  surface.  01   the     ilbiallS    pOStCriOr.       1116 


I 


THE  TIBIA 


remaining  part  of  the  posterior  surface  is  smooth  and  covered  by  the  Tibialis 
posterior.  Flexor  digitorum  longus,  and  Flexor  hallucis  longus.  Immediately  below 
the  popliteal  line  is  the  nutrient  foramen,  which  is  large  and  directed  obliquely 
downward. 

The  Lower  Extremity  (distal  extremity). — The  lower  extremity,  much  smaller 
than  the  upper,  presents  five  surfaces;  it  is  prolonged  downward  on  its  medial 
side  as  a  strong  process,  the  medial  malleolus. 

Surfaces. — The  inferior  articular  surface  is  quadrilateral,  and  smooth  for  articu- 
lation with  the  talus.  It  is  concave  from  before  backward,  broader  in  front  than 
behind,  and  traversed  from  before  backward  by  a  slight  elevation,  separating 
two  depressions.    It  is  continuous  with  that  on  the  medial  malleolus. 


Upper  extremity 


Appears  before  or 
shortly  after  birth 


Joins  body 
abovi  20lh  year 


Joins  body  about 
I8th  year 


Lower  extremity 


'Fig.  260. 


-Plan  of  ossification  of  the  tibia, 
centers. 


From  three 


Fig.  261. — Epiphysial  lines  of  tibia  and  fibula 
in  a  young  adult.     Anterior  aspect. 


The  anterior  surface  of  the  lower  extremity  is  smooth  and  rounded  above,  and 
covered  by  the  tendons  of  the  Extensor  muscles;  its  lower  margin  presents  a  rough 
transverse  depression  for  the  attachment  of  the  articular  capsule  of  the  ankle- 
joint. 

The  posterior  surface  is  traversed  by  a  shallow  groove  directed  obliquely  down- 
ward and  medialward,  continuous  with  a  similar  groove  on  the  posterior  surface 
I  of  the  talus  and  serving  for  the  passage  of  the  tendon  of  the  Flexor  hallucis  longus. 

The  lateral  surface  presents  a  triangular  rough  depression  for  the  attachment 
[of  the  inferior  interosseous  ligament  connecting  it  with  the  fibula;  the  lower  part 
of  this  depression  is  smooth,  covered  with  cartilage  in  the  fresh  state,  and  articu- 
lates with  the  fibula.  The  surface  is  bounded  by  two  prominent  borders,  con- 
pnuous  above  with  the  interosseous  crest;  they  afford  attachment  to  the  anterior 
[and  posterior  ligaments  of  the  lateral  malleolus. 

The  medial  surface  is  prolonged  downward  to  form  a  strong  pyramidal  process, 

[flattened  from  without  inward — the  medial  malleolus.  The  medial  surface  of  this 

[process  is  convex  and  subcutaneous;  its  lateral  or  articular  surface  is  smooth  and 

lightly  concave,  and  articulates  with  the  talus;  its  anterior  border  is  rough,  for 


260  OSTEOLOGY 

the  attachment  of  the  anterior  fibers  of  the  deltoid  ligament  of  the  ankle-joint; 
its  posterior  border  presents  a  broad  groove,  the  malleolar  sulcus,  directed  obliquely 
downward  and  medial  ward,  and  occasionally  double;  this  sulcus  lodges  the  tendons 
of  the  Tibialis  posterior  and  Flexor  digitorum  longus.  The  summit  of  the  medial 
malleolus  is  marked  by  a  rough  depression  behind,  for  the  attachment  of  the 
deltoid  ligament. 

Structure. — The  structure  of  the  tibia  is  like  that  of  the  other  long  bones.  The  compact  wall 
of  the  body  is  thickest  at  the  junction  of  the  middle  and  lower  thirds  of  the  bone. 

Ossification. — The  tibia  is  ossified  from  three  centers  (Figs.  260,  261):  one  for  the  body  and 
one  for  either  extremity.  Ossification  begins  in  the  center  of  the  body,  about  the  seventh  week 
of  fetal  life,  and  gradually  extends  toward  the  extremities.  The  center  for  the  upper  epiphysis 
appears  before  or  shortly  after  birth;  it  is  flattened  in  form,  and  has  a  thin  tongue-shaped  process 
in  front,  which  forms  the  tuberosity  (Fig.  2t30) ;  that  for  the  lower  epiphysis  appears  in  the  second 
year.  The  lower  epiphysis  joins  the  body  at  about  the  eighteenth,  and  the  upper  one  joins  about 
the  twentieth  year.  Two  additional  centers  occasionally  exist,  one  for  the  tongue-shaped  process 
of  the  upper  epiphysis,  which  forms  the  tuberosity,  and  one  for  the  medial  malleolus. 

The  Fibula  (Calf  Bone). 

The  fibula  (Figs.  258,  259)  is  placed  on  the  lateral  side  of  the  tibia,  with  which 
it  is  connected  above  and  below.  It  is  the  smaller  of  the  two  bones,  and,  in 
proportion  to  its  length,  the  most  slender  of  all  the  long  bones.  Its  upper 
extremity  is  small,  placed  toward  the  back  of  the  head  of  the  tibia,  below  the  level 
of  the  knee-joint,  and  excluded  from  the  formation  of  this  joint.  Its  lower  extremity 
inclines  a  little  forward,  so  as  to  be  on  a  plane  anterior  to  that  of  the  upper  end; 
it  projects  below  the  tibia,  and  forms  the  lateral  part  of  the  ankle-joint.  The 
bone  has  a  body  and  two  extremities. 

The  Upper  Extremity  or  Head  (capitulum  fibulw;  proximal  extremity). — The 
upper  extremity  is  of  an  irregular  quadrate  form,  presenting  above  a  flattened 
articular  surface,  directed  upward,  forward,  and  medialward,  for  articulation  with 
a  corresponding  surface  on  the  lateral  condyle  of  the  tibia.  On  the  lateral  side 
is  a  thick  and  rough  prominence  continued  behind  into  a  pointed  eminence,  the 
apex  {styloid  process),  which  projects  upward  from  the  posterior  part  of  the  head. 
The  prominence,  at  its  upper  and  lateral  part,  gives  attachment  to  the  tendon  of 
the  Biceps  femoris  and  to  the  fibular  collateral  ligament  of  the  knee-joint,  the  liga- 
ment dividing  the  tendon  into  two  parts.  The  remaining  part  of  the  circumference 
of  the  head  is  rough,  for  the  attachment  of  muscles  and  ligaments.  It  presents  in 
front  a  tubercle  for  the  origin  of  the  upper  and  anterior  fibers  of  the  Perona^us 
longus,  and  a  surface  for  the  attachment  of  the  anterior  ligament  of  the  head; 
and  behind,  another  tubercle,  for  the  attachment  of  the  posterior  ligament  of  the 
head  and  the  origin  of  the  upper  fibers  of  the  Soleus. 

The  Body  or  Shaft  {corpus  fibidce). — The  body  presents  four  borders — the 
antero-lateral,  the  antero-medial,  the  postero-lateral,  and  the  postero-medial ;  and 
four  surfaces — anterior,  posterior,  medial,  and  lateral. 

Borders. — The  antero-lateral  border  begins  above  in  front  of  the  head,  runs  ver- 
tically downward  to  a  little  below  the  middle  of  the  bone,  and  then  curving  some- 
what lateralward,  bifurcates  so  as  to  embrace  a  triangular  subcutaneous  surface 
immediately  above  the  lateral  malleolus.  This  border  gives  attachment  to  an 
intermuscular  septum,  which  separates  the  Extensor  muscles  on  the  anterior 
surface  of  the  leg  from  the  Peronaei  longus  and  brevis  on  the  lateral  surface. 

The  antero-medial  border,  or  interosseous  crest,  is  situated  close  to  the  medial 
side  of  the  preceding,  and  runs  nearly  parallel  with  it  in  the  upper  third  of  its 
extent,  but  diverges  from  it  in  the  lower  two-thirds.  It  begins  above  just  beneath 
the  head  of  the  bone  (sometimes  it  is  quite  indistinct  for  about  2.5  cm.  below  the 
head),  and  ends  at  the  apex  of  a  rough  triangular  surface  immediately  above  the 


THE  FIBULA 


261 


articular  facet  of  the  lateral  malleolus.  It  serves  for  the  attachment  of  the  inter- 
osseous membrane,  which  separates  the  Extensor  muscles  in  front  from  the  Flexor 
muscles  behind. 

The  postero-lateral  border  is  prominent;  it  begins  above  at  the  apex,  and  ends 
below  in  the  posterior  border  of  the  lateral  malleolus.  It  is  directed  lateralward 
above,  backward  in  the  middle  of  its  course,  backward,  and  a  little  medialward 
below,  and  gives  attachment  to  an  aponeurosis  which  separates  the  Peronsei  on 
the  lateral  surface  from  the  Flexor  muscles  on  the  posterior  surface. 

The  postero-medial  border,  sometimes  called  the  oblique  line,  begins  above  at  the 
medial  side  of  the  head,  and  ends  by  becoming  continuous  with  the  interosseous 
crest  at  the  lower  fourth  of  the  bone.  It  is  well-marked  and  prominent  at  the  upper 
and  middle  parts  of  the  bone.  It  gives  attachment  to  an  aponeurosis  which  sep- 
arates the  Tibialis  posterior  from  the  Soleus  and  Flexor  hallucis  longus. 


Upper  extremity 


Interossecms 
crest 


Appears  about _ 
4.th  year 


Unites  about 
25th  year 


For  posterior 
talofbular  ligt. 


Appears  at 
2nd  year 


Unites  about 
20th  year 


Lower  extremity 


Fia.  262. — Lower  extremity  of  right  fibula. 
Medial  aspect. 


Fig.    263. — Plan  of  ossification   of  tlie 
fibula.     From  three  centers. 


Surfaces. — The  anterior  surface  is  the  interval  between  the  antero-lateral  and 
antero-medial  borders.  It  is  extremely  narrow  and  flat  in  the  upper  third  of  its 
extent;  broader  and  grooved  longitudinally  in  its  lower  third;  it  serves  for  the 
origin  of  three  muscles:  the  Extensor  digitorum  longus,  Extensor  hallucis  longus, 
and  Peronseus  tertius. 

The  posterior  surface  is  the  space  included  between  the  postero-lateral  and  the 
postero-medial  borders;  it  is  continuous  below  with  the  triangular  area  above 
the  articular  surface  of  the  lata-al  malleolus;  it  is  directed  backward  above,  back- 
ward and  medialward  at  its  middle,  directly  medialward  below.  Its  upper  third 
is  rough,  for  the  origin  of  the  Soleus;  its  lower  part  presents  a  triangular  surface, 
connected  to  the  tibia  by  a  strong  interosseous  ligament;  the  intervening  part  of 
the  surface  is  covered  by  the  fibers  of  origin  of  the  Flexor  hallucis  longus.  Near 
the  middle  of  this  surface  is  the  nutrient  foramen,  which  is  directed  downward. 

The  medial  surface  is  the  interval  included  between  the  antero-medial  and  the 
postero-medial  borders.     It  is  grooved  for  the  origin  of  the  Tibialis  posterior. 


OSTEOLOGY 


The  lateral  surface  is  the  space  between  the  antero-lateral  and  postero-lateral 
borders.  It  is  broad,  and  often  deeply  grooved;  it  is  directed  lateralward  in  the 
upper  two-thirds  of  its  course,  backward  in  the  lower  third,  where  it  is  continuous 
with  the  posterior  border  of  the  lateral  malleolus.  This  surface  gives  origin  to 
the  Peronsei  longus  and  brevis. 

The  Lower  Extremity  or  Lateral  Malleolus  (malleolus  lateralis;  distal  extremity; 
external  malleolus). — The  lower  extremity  is  of  a  pyramidal  form,  and  somewhat 
flattened  from  side  to  side;  it  descends  to  a  lower  level  than  the  medial  malleolus. 
The  lateral  surface  is  convex,  subcutaneous,  and  continuous  with  the  triangular, 
subcutaneous  surface  on  the  lateral  side  of  the  body.  The  medial  surface  (Fig. 
262)  presents  in  front  a  smooth  triangular  surface,  convex  from  above  downward, 
which  articulates  with  a  corresponding  surface  on  the  lateral  side  of  the  talus. 
Behind  and  beneath  the  articular  surface  is  a  rough  depression,  w^hich  gives  attach- 
ment to  the  posterior  talofibular  ligament.  The  anterior  border  is  thick  and  rough, 
and  marked  below  by  a  depression  for  the  attachment  of  the  anterior  talofibular 
ligament.  The  posterior  border  is  broad  and  presents  the  shallow  malleolar  sulcus, 
for  the  passage  of  the  tendons  of  the  Peronsei  longus  and  brevis.  The  summit 
is  rounded,  and  give  attachment  to  the  calcaneofibular  ligament. 

Ossification. — The  fibula  is  ossified  from  three  centers  (Fig.  263) :  one  for  the  body,  and  one 
for  either  end.  Ossification  begins  in  the  body  about  the  eighth  week  of  fetal  Ufe,  and  extends 
toward  the  extremities.  At  birth  the  ends  are  cartilaginous.  Ossification  commences  in  the 
lower  end  in  the  second  year,  and  in  the  upper  about  the  fourth  year.  The  lower  epiphysis, 
the  first  to  ossify,  unites  with  the  body  about  the  twentieth  year;  the  upper  epiphysis  joins 
about  the  twenty-fifth  year. 

Groove  for  PeroncBUs  longus 


Trochlear  process 

Middle  articular  surface 
Anterior  artic.  surface 
Post,  artic.  surface 


Trochlear  process 

For  cuboid  bone 
For  attachment 

of  plantar  calcaneo- 
cuboid ligament 

Sustentaculum 
tali 


Sustentaculum.  Sulcus  for  Flexor 

'*"  haUu^is  longus 


Sulcus  calcanei 


Tuberosity 
Fio.  264.— Left  calcaneus,  superior  surface. 


Medial  process 

Tuberosity 

Lateral  process 
Fig.  265. — Left  calcaneus,  inferior  surface. 


THE    FOOT. 

The  skeleton  of  the  foot  (Figs.  268  and  269)  consists  of  three  parts:  the  tarsus, 
metatarsus,  and  phalanges. 


THE  TARSUS 


The  Tarsus  (Ossa  Tarsi). 


263 


The  tarsal  bones  are  seven  in  number,  viz.,  the  calcaneus,  talus,  cuboid,  navicular, 
and  the  first,  second,  and  third  cuneiforms. 

The  Calcaneus  (os  calcis)  (Figs.  264  to  267).— The  calcaneus  is  the  largest  of  the 
tarsal  bones.  It  is  situated  at  the  lower  and  back  part  of  the  foot,  serving  to 
transmit  the  weight  of  the  body  to  the  ground,  and  forming  a  strong  lever  for 
the  muscles  of  the  calf.  It  is  irregularly  cuboidal  in  form,  having  its  long  axis 
directed  forward  and  lateralward;  it  presents  for  examination  six  surfaces. 


Sulcus  calcanei 
Middle  articular  surface  for  talus 


Posterior  articular  surface  for  talus 


Trochlear  process 
Groove  for  Peronaeus  longua 


Lateral  process' 


Tuberosity 


Fig.  266. — Left  calcaneus,  lateral  surface. 


Middle  articular  surface  for  talus 
Sustentaculum  tali 
Posterior  articular  surface  for  talus 


Tuberosity 


Anterior  articxdar  surface 
for  talus 


Sulcus  for  Flexor 
hallucis  longus 
Medial  process 


Fig.  267. — Left  calcaneus,  medial  surface. 


For  cuboid  bone 


Surfaces. — The  superior  surface  extends  behind  on  to  that  part  of  the  bone  which 
projects  backward  to  form  the  heel.  This  varies  in  length  in  different  individuals, 
is  convex  from  side  to  side,  concave  from  before  backward,  and  supports  a  mass  of 
fat  placed  in  front  of  the  tendo  calcaneus.  In  front  of  this  area  is  a  large  usually 
somewhat  oval-shaped  facet,  the  posterior  articular  surface,  which  looks  upward 
and  forward;  it  is  convex  from  behind  forward,  and  articulates  with  the  posterior 
calcaneal  facet  on  the  under  surface  of  the  talus.  It  is  bounded  anteriorly  by  a 
deep  depression  which  is  continued  backward  and  medialward  in  the  form  of  a 
groove,  the  calcaneal  sulcus.  In  the  articulated  foot  this  sulcus  lies  below  a  similar 
one  on  the  under  surface  of  the  talus,  and  the  two  form  a  canal  (sinus  tarsi)  for  the 


264 


OSTEOLOGY 


Groove  for  tendon  of 
Peron^u8   long  us 


Groove  for  tendon  of 

.   PEEON^rs     BREVIS 


Peron^us  teetitb 

PERONiETJS     BEEVIS 


Groove  for  tendon  of 
Flexor  hallucis  longps 


TarsiLS 


Metatarsus 


-Ext.  niGiTORCM  brevis 


Phalanges 


Ext.  HALLrcis  longus 


Fia.  268. — Bones  of  the  right  foot.     Dorsal  surface. 


TARSUS 


265 


Abductor  halluois 
Medial  head  or 


Flexor  hallucis  urkvis 


Tvbercle  of 
navicular 


Tibialis  anterior 


Tvx)  sesamoid 
bones 


Lateral  head  of  quadratus 

PLANTS 


Flexor  brevis 
AND  Abductor 

DIGITI  QUINTI 


Flexor  digitorum 

BREVIS 


Flexor  digitorum 

LONQUS 


FiQ.  269. — Bones  of  the  right  foot.     Plantar  surface. 


OSTEOLOGY 


lodgement  of  the  interosseous  talocalcaneal  ligament.  In  front  and  to  the  medial 
side  of  this  groove  is  an  elongated  facet,  concave  from  behind  forward,  and  with  its 
long  axis  directed  forward  and  lateralward.  This  facet  is  frequently  divided  into 
two  by  a  notch :  of  the  two,  the  posterior,  and  larger  is  termed  the  middle  articular 
surface;  it  is  supported  on  a  projecting  process  of  bone,  the  sustentaculum  tali, 
and  articulates  with  the  middle  calcaneal  facet  on  the  under  surface  of  the  talus; 
the  anterior  articular  surface  is  placed  on  the  anterior  part  of'  the  body,  and  articu- 
lates with  the  anterior  calcaneal  facet  on  the  talus.  The  upper  surface,  anterior 
and  lateral  to  the  facets,  is  rough  for  the  attachment  of  ligaments  and  for  the  origin 
of  the  Extensor  digitorum  brevis. 

The  inferior  or  plantar  surface  is  uneven,  wider  behind  than  in  front,  and  convex 
from  side  to  side;  it  is  bounded  posteriorly  by  a  transverse  elevation,  the  calcaneal 
tuberosity,  which  is  depressed  in  the  middle  and  prolonged  at  either  end  into  a 
process;  the  lateral  process,  small,  prominent,  and  rounded,  gives  origin  to  part 
of  the  Abductor  digiti  quinti;  the  medial  process,  broader  and  larger,  gives  attach- 
ment, by  its  prominent  medial  margin,  to  the  Abductor  hallucis,  and  in  front 
to  the  Flexor  digitorum  brevis  and  the  plantar  aponeurosis ;  the  depression  between 
the  processes  gives  origin  to  the  Abductor  digiti  quinti.  The  rough  surface  in 
front  of  the  processes  gives  attachment  to  the  long  plantar  ligament,  and  to  the 
lateral  head  of  the  Quadratus  plantse;  while  to  a  prominent  tubercle  nearer  the 
anterior  part  of  this  surface,  as  well  as  to  a  transverse  groove  in  front  of  the  tubercle, 
is  attached  the  plantar  calcaneocuboid  ligament. 

The  lateral  surface  is  broad  behind  and  narrow  in  front,  flat  and  almost  sub- 
cutaneous; near  its  center  is  a  tubercle,  for  the  attachment  of  the  calcaneofibular 
ligament.  At  its  upper  and  anterior  part,  this  surface  gives  attachment  to  the 
lateral  talocalcaneal  ligament;  and  in  front  of  the  tubercle  it  presents  a  narrow 
surface  marked  by  two  oblique  grooves.  The  grooves  are  separated  by  an  elevated 
ridge,  or  tubercle,  the  trochlear  process  {peroneal  tubercle),  which  varies  much  in 
size  in  different  bones.  The  superior  groove  transmits  the  tendon  of  the  Perona^us 
brevis;  the  inferior  groove,  that  of  the  Perona^us  longus. 

The  medial  surface  is  deeply  concave;  it  is  directed  obliquely  downward  and 
forward,  and  serves  for  the  transmission  of  the  plantar  vessels  and  nerves  into  the 
sole  of  the  foot;  it  affords  origin  to  part  of  the  Quadratus  plantee.  At  its  upper 
and  forepart  is  a  horizontal  eminence,  the  sustentaculum  tali,  which  gives  attach- 
ment to  a  slip  of  the  tendon  of  the  Tibialis  posterior.  This  eminence  is  concave 
above,  and  articulates  with  the  middle  calcaneal  articular  surface  of  the  talus; 
below,  it  is  grooved  for  the  tendon  of  the  Flexor  hallucis  longus ;  its  anterior  margin 
gives  attachment  to  the  plantar  calcaneonavicular  ligament,  and  its  medial, 
to  a  part  of  the  deltoid  ligament  of  the  ankle-joint. 

The  anterior  or  cuboid  articular  surface  is  of  a  somewhat  triangular  form.  It  is 
concave  from  above  downward  and  lateralward,  and  convex  in  a  direction  at  right 
angles  to  this.  Its  medial  border  gives  attachment  to  the  plantar  calcaneonavicular 
ligament. 

The  posterior  surface  is  prominent,  convex,  wider  below  than  above,  and  divisible 
into  three  areas.  The  lowest  of  these  is  rough,  and  covered  by  the  fatty  and  fibrous 
tissue  of  the  heel;  the  middle,  also  rough,  gives  insertion  to  the  tendo  calcaneus 
and  Plantaris;  while  the  highest  is  smooth,  and  is  covered  by  a  bursa  which  inter- 
venes between  it  and  the  tendo  calcaneus. 

Articulations. — The  calcaneus  articulates  with  two  bones:    the  talus  and  xjuboid. 

The  Talus  {astragalus;  ankle  hone)  (Figs.  270  to  273). — The  talus  is  the  second 
largest  of  the  tarsal  bones.  It  occupies  the  middle  and  upper  part  of  the  tarsus, 
supporting  the  tibia  above,  resting  upon  the  calcaneus  below,  articulating  on 
either  side  with  the  malleoli,  and  in  front  with  the  navicular.  It  consists  of  a 
body,  a  neck,  and  a  head 


THE  TARSUS 


267 


The  Body  (corpus  tali). — ^The  superior  surface  of  the  body  presents,  behind,  a 
smooth  trochlear  surface,  the  trochlea,  for  articulation  with  the  tibia.  The  trochlea 
is  broader  in  front  than  behind,  convex  from  before  backward,  slightly  concave 
from  side  to  side:  in  front  it  is  continuous  with  the  upper  surface  of  the  neck  of 
the  bone. 

For  medial  malleolus 
Head 
Neck 


For  lateral  m,aUeolus 
For  inferior  transverse  ligarnent 


Medial  tubercle 
Sulcus  for  Flexor  Iiailucis  longus 


Trochlea  for  tibia 
Lateral  tubercle 

Fig.  270. — Left  talus,  from  above. 


For  plantar  calcaneonavicular  ligament 
For  navicular  bone 

Anterior  calcaneal  articular  surface 


Sulcus  tali 


^Posterior  calcaneal  articular 
surface 


Lateral  tubercle 
Sulcus  for  Flexor  hallucis  longus 
Middle  calcaneal  articular  surface 
Fig.  271. — Left  talus,  from  below. 


The  inferior  surface  presents  two  articular  areas,  the  posterior  and  middle  cal- 
janeal  surfaces,  separated  from  one  another  by  a  deep  groove,  the  sulcus  tali. 
The  groove  runs  obliquely  forward  and  lateralward,  becoming  gradually  broader 
ind  deeper  in  front:  in  the  articulated  foot  it  lies  above  a  similar  groove  upon 
he  upper  surface  of  the  calcaneus,  and  forms,  with  it,  a  canal  (sinus  tarsi)  filled 


268 


OSTEOLOGY 


up  in  the  fresh  state  by  the  interosseous  talocalcaneal  ligament.  The  posterior 
calcaneal  articular  surface  is  large  and  of  an  oval  or  oblong  form.  It  articulates 
with  the  corresponding  facet  on  the  upper  surface  of  the  calcaneus/  and  is  deei)ly 
concave  in  the  direction  of  its  long  axis  which  runs  forward  and  lateralward  at 
an  angle  of  about  45°  with  the  median  plane  of  the  body.  The  middle  calcaneal 
articular  surface  is  small,  oval  in  form  and  slightly  convex;  it  articulates  with  the 
upper  surface  of  the  sustentaculum  tali  of  the  calcaneus. 

The  medial  surface  presents  at  its  upper  part  a  pear-shaped  articular  facet  for 
the  medial  malleolus,  continuous  above  with  the  trochlea;  below  the  articular 
surface  is  a  rough  depression  for  the  attachment  of  the  deep  portion  of  the  deltoid 
ligament  of  the  ankle-joint. 


Trochlea  for  tibia 


For  medial  malleolus 


hieck 


Sulcus  for  Flex.  haUucis  longus 


For  navicular  hone 

'  For  plantar  calcaneonavicular  ligament 
Fig.  272. — Left  talus,  medial  surface. 


Trochlea  for  tibia 


For  lateral  malleolus 


Sulcus  tali 


Posterior  calcaneal  articular 
surface 


Anterior  calcaneal  articular  surface 
For  navicular  hone 

Fig.  273. — Left  talus,  lateral  surface. 

The  lateral  surface  carries  a  large  triangular  facet,  concave  from  above  downward, 
for  articulation  with  the  lateral  malleolus;  its  anterior  half  is  continuous  above  with 
the  trochlea;  and  in  front  of  it  is  a  rough  depression  for  the  attachment  of  the  ante- 
rior talofibular  ligament.  Between  the  posterior  half  of  the  lateral  border  of  the 
trochlea  and  the  posterior  part  of  the  base  of  the  fibular  articular  surface  is  a  tri- 
angular facet  (Fawcett^)  which  comes  into  contact  with  the  transverse  inferior 
tibiofibular  ligament  during  flexion  of  the  ankle-joint;  below  the  base  of  this  facet 
is  a  groove  which  affords  attachment  to  the  posterior  talofibular  ligament. 

The  posterior  surface  is  narrow,  and  traversed  by  a  groove  running  obliquely 

'  Sewell  (Journal  of  Anatomy  and  Physiology,  vol.  xxxviii)  pointed  out  that  in  about  10  per  cent,  of  bones  a  small 
triangular  facet,  continuous  with  the  posterior  calcaneal  facet,  is  present  at  the  junction  of  the  lateral  surface  of  the 
body  with  the  posterior  wall  of  the  .sulcus  tali. 

-  Edinburgh  Medical  Journal,  1895. 


i 


THE  TARSUS 


269 


downward  and  medialward,  and  transmitting  the  tendon  of  the  Flexor  hallucis 
longus.  Lateral  to  the  groove  is  a  prominent  tubercle,  the  posterior  process,  to 
which  the  posterior  talofibular  ligament  is  attached;  this  process  is  sometimes 
separated  from  the  rest  of  the  talus,  and  is  then  known  as  the  os  trigonum.  Medial 
to  the  groove  is  a  second  smaller  tubercle. 

The  Neck  {collum  tali). — The  neck  is  directed  forward  and  medialward,  and. 
comprises  the  constricted  portion  of  the  bone  between  the  body  and  the  oval  head. 
Its  upper  and  medial  surfaces  are  rough,  for  the  attachment  of  ligaments;  its  lateral 
surface  is  concave  and  is  continuous  below  with  the  deep  groove  for  the  inter- 
osseous talocalcaneal  ligament. 

The  Head  (caput  tali). — The  head  looks  forward  and  medialward;  its  anterior 
articular  or  navicular  surface  is  large,  oval,  and  convex.  Its  inferior  surface  has  two 
facets,  which  are  best  seen  in  the  fresh  condition.  The  medial,  situated  in  front 
of  the  middle  calcaneal  facet,  is  convex,  triangular,  or  semi-oval  in  shape,  and 
rests  on  the  plantar  calcaneonavicular  ligament;  the  lateral,  named  the  anterior 
calcaneal  articular  surface,  is  somewhat  flattened,  and  articulates  with  the  facet  on 
the  upper  surface  of  the  anterior  part  of  the  calcaneus. 

Articulations. — The  talus  articulates  with,  four  bones:    tibia,  fibula,  calcaneus,  and  navicular. 

The  Cuboid  Bone  (os  cuboideum)  (Figs.  274,  275) . — The  cuboid  bone  is  placed  on 
the  lateral  side  of  the  foot,  in  front  of  the  calcaneus,  and  behind  the  fourth  and  fifth 
metatarsal  bones.    It  is  of  a  pyramidal  shape,  its  base  being  directed  medialward. 


For  3rd  cuneiform        For  4th  metatarsal 


For  Uh 
metatarsal 


Peronceal       Tuberosity  For  calcaneus 
evlcus 


Fig.  274. — The  left  cuboid.     Antero-medial  view. 


Fig.  275. — The  left  cuboid.     Postero-lateral  view. 


Surfaces. — The  dorsal  surface,  directed  upward  and  lateralward,  is  rough,  for  the 
ittachment  of  ligaments.  The  plantar  surface  presents  in  front  a  deep  groove, 
Jie  peroneal  sulcus,  which  runs  obliquely  forward  and  medialward;  it  lodges  the 
;<indon  of  the  Peronseus  longus,  and  is  bounded  behind  by  a  prominent  ridge, 
fO  which  the  long  plantar  ligament  is  attached.  The  ridge  ends  laterally  in  an 
^ininence,  the  tuberosity,  the  surface  of  which  presents  an  oval  facet;  on  this  facet 
tUdes  the  sesamoid  bone  or  cartilage  frequently  found  in  the  tendon  of  the  Pero- 

?us  longus.  The  surface  of  bone  behind  the  groove  is  rough,  for  the  attachment 
\l  the  plantar  calcaneocuboid  ligament,  a  few  fibers  of  the  Flexor  hallucis  brevis, 
md  a  fasciculus  from  the  tendon  of  the  Tibialis  posterior.  The  lateral  surface 
p>resents  a  deep  notch  form.ed  by  the  commencement  of  the  peroneal  sulcus.  The 
posterior  surface  is  smooth,  triangular,  and  concavo-convex,  for  articulation  with 
the  anterior  surface  of  the  calcaneus;  its  infero-medial  angle  projects  backward 
as  a  process  which  underlies  and  supports  the  anterior  end  of  the  calcaneus.  The 
anterior  surface,  of  smaller  size,  but  also  irregularly  triangular,  is  divided  by  a 
vertical  ridge  into  two  facets:  the  medial,  quadrilateral  in  form,  articulates  with 
the  fourth  metatarsal;  the  lateral,  larger  and  more  triangular,  articulates  with  the 
fifth.  The  medial  surface  is  broad,  irregularly  quadrilateral,  and  presents  at 
its  middle  and  upper  part  a  smooth  oval  facet,  for  articulation  with  the  third 


I 


270 


OSTEOLOGY 


cuneiform;  and  behind  this  (occasionally)  a  smaller  facet,  for  articulation  with 
the  navicular;  it  is  rough  in  the  rest  of  its  extent,  for  the  attachment  of  strong 
interosseous  ligaments. 

Articulations. — The  cuboid  articulates  with /our  bones:  the  calcaneus,  third  cuneiform,  jind 
fourth  and  fifth  metatarsals;  occasionally  with  a  fifth,  the  navicular. 

The  Navicular  Bone  {os  naviculare  pedis;  scaphoid  bone)  (Figs.  276,  277). — The 
navicular  bone  is  situated  at  the  medial  side  of  the  tarsus,  between  the  talus 
behind  and  the  cuneiform  bones  in  front. 


For  1st  cuneijorm 


For  2iid  cuneiforvi 


For  3rd 

cuneiform 


Fig.  276.— The  left  naviciilar. 


Occasional 
facet  for 
cvboid 
Antero-lateral  view. 


For  talus        Tuberosity 
Fig.  277. — Theleft  navicular.     Postero-niedialview. 


Surfaces. — The  anterior  surface  is  convex  from  side  to  side,  and  subdivided  by  two 
ridges  into  three  facets,  for  articulation  with  the  three  cuneiform  bones.  The 
posterior  surface  is  oval,  concave,  broader  laterally  than  medially,  and  articulates 
with  the  rounded  head  of  the  talus.  The  dorsal  surface  is  convex  from  side  to  side, 
and  rough  for  the  attachment  of  ligaments.  The  plantar  surface  is  irregular,  and 
also  rough  for  the  attachment  of  ligaments.    The  medial  surface  presents  a  rounded 

tuberosity,  the  lower  part  of  which 
Fcr  2nd  For  gives  attachment  to  part  of  the 

For  1st  metatarsal  metatarsal       2nd  cuneiform       tendon  of  the  Tibialis  posterior. 

The  lateral  surface  is  rough  and 
irregular  for  the  attachment  of 
ligaments,  and  occasionally  pre- 
sents a  small  facet  for  articula- 
tion with  the  cuboid  bone. 

Articulations. — Thenavicular  articu- 
lates with  four  bones:  the  talus  and 
the  three  cuneiforms;  occasionally  with 
a  fifth,  the  cuboid. 


For  tendon  of 
Tibialis  anterior 


For  navicular 


Fig.  278. — The  left  first  cunei- 
form.    Antero-medial  view. 


The  First  Cuneiform  Bone  {os 

cvneiform  privium;  internal ciinei- 
''form.''-roSrifii\?;fi  vTw'-    fomi)  (Figs.  278,  _279).-The  first 

cuneiform  bone  is  the  largest  of 
the  three  cuneiforms.  It  is  situated  at  the  medial  side  of  the  foot,  between  the 
navicular  behind  and  the  base  of  the  first  metatarsal  in  front. 

Surf aces.^ — ^Tlie  medial  surface  is  subcutaneous,  broad,  and  quadrilateral ;  at  its 
anterior  plantar  angle  is  a  smooth  oval  impression,  into  which  part  of  the  tendon 
of  the  Tibialis  anterior  is  inserted;  in  the  rest  of  its  extent  it  is  rough  for  the 
attachment  of  ligaments.  The  lateral  surface  is  concave,  presenting,  along  its 
superior  and  posterior  borders  a  narrow  F-shaped  surface,  the  vertical  limb  and 
posterior  part  of  the  horizontal  limb  of  which  articulate  with  the  second  cuneiform, 
while  the  anterior  part  of  the  horizontal  limb  articulates  with  the  second  metatarsal 


THE  TARSUS 


271 


bone :  the  rest  of  this  surface  is  rough  for  the  attachment  of  ligaments  and  part 
of  the  tendon  of  the  Peronaeus  longus.  The  anterior  surface,  kidney-shaped  and 
much  larger  than  the  posterior,  articulates  with  the  first  metatarsal  bone.  The 
posterior  surface  is  triangular,  concave,  and  articulates  with  the  most  medial  and 
largest  of  the  three  facets  on  the  anterior  surface  of  the  navicular.  The  plantar 
surface  is  rough,  and  forms  the  base  of  the  wedge;  at  its  back  part  is  a  tuberosity 
for  the  insertion  of  part  of  the  tendon  of  the  Tibialis  posterior.  It  also  gives 
insertion  in  front  to  part  of  the  tendon  of  the  Tibialis  anterior.  The  dorsal  surface 
is  the  narrow  end  of  the  wedge,  and  is  directed  upward  and  lateralward;  it  is 
rough  for  the  attachment  of  ligaments. 

Articulations. — The  first  cuneiform  articulates  with  four  bones:  the  navicular,  second  cunei- 
form, and  first  and  second  metatarsals. 

The  Second  Cuneiform  Bone  (os  cuneiforme  secundum;  middle  cuneiform)  (Figs. 
280,  281).— The  second  cuneiform  bone,  the  smallest  of  the  three,  is  of  very  reg- 
ular wedge-like  form,  the  thin  end  being  directed  downward.  It  is  situated  between 
the  other  two  cuneiforms,  and  articulates  with  the  navicular  behind,  and  the 
second  metatarsal  in  front. 

-  Surfaces. — The  anterior  surface,  triangular  in  form,  and  narrower  than  the  pos- 
terior, articulates  with  the  base  of  the  second  metatarsal  bone.  The  posterior  sur- 
face, also  triangular,  articulates  with  the  intermediate  facet  on  the  anterior  surface 
of  the  navicular.  The  medial  surface  carries  an  L-shaped  articular  facet,  running 
along  the  superior  and  posterior  borders,  for  articulation  w^ith  the  first  cuneiform, 
and  is  rough  in  the  rest  of  its  extent  for  the  attachment  of  ligaments.    The  lateral 


For  1st  cuneiform 


For  navicular 


For  2nd  metatarsal  For  3rd  cuneiform 


Fig.  280.— The  left  second 
ctineiform.  An  t  ero-media  1 
vi  'w. 


Fig.  281.— The  left 
second  cuneiform.  Pos- 
tero-lateral  view. 


surface  presents  posteriorly  a  smooth 
facet  for  articulation  with  the  third 
cuneiform  bone.  The  dorsal  surface 
forms  the  base  of  the  wedge;  it  is 
quadrilateral  and  rough  for  the  at- 
tachment of  ligaments.  The  plantar 
surface,  sharp  and  tuberculated,  is 
also  rough  for  the  attachment  of 
ligaments,  and  for  the  insertion  of  a 
slip  from  the  tendon  of  the  Tibialis 
posterior. 

Articulations. — The  second  cuneiform  articulates  with  four  bones:  the  navicular,  first  and 
tl  ird  cuneiforms,  and  second  metatarsal. 

The  Third  Cuneiform  Bone  {os  cuneiforme  iertium;  external  cuneiform)  (Figs.  282, 
2S3). — The  third  cuneiform  bone,  intermediate  in  size  between  the  two  preceding, 
is  wedge-shaped,  the  base  being  uppermost.  It  occupies  the  center  of  the  front  row 
ol  the  tarsal  bones,  between  the  second  cuneiform  medially,  the  cuboid  laterally, 
the  navicular  behind,  and  the  third  metatarsal  in  front. 

Surfaces. — The  anterior  surface,  triangular  in  form,  articulates  with  the  third 
metatarsal  bone.  The  posterior  surface  articulates  with  the  lateral  facet  on  the 
anterior  surface  of  the  navicular,  and  is  rough  below  for  the  attachment  of  liga- 
mentous fibers.  The  medial  surface  presents  an  anterior  and  a  posterior  articular 
facet,  separated  by  a  rough  depression:  the  anterior,  sometimes  divided,  articulates 
with  the  lateral  side  of  the  base  of  the  second  metatarsal  bone;  the  posterior  skirts 
tl  e  posterior  border,  and  articulates  with  the  second  cuneiform;  the  rough  depres- 
sion gives  attachment  to  an  interosseous  ligament.  The  lateral  surface  also  pre- 
sents two  articular  facets,  separated  by  a  rough  non-articular  area;  the  anterior 
facet,  situated  at  the  superior  angle  of  the  bone,  is  small  and  semi-oval  in  shape, 
and  articulates  with  the  medial  side  of  the  base  of  the  fourth  metatarsal  bone; 


272 


OSTEOLOGY 


the  posterior  and  larger  one  is  triangular  or  oval,  and  articulates  with  the  cuboid; 
the  rough,  non-articular  area  serves  for  the  attachment  of  an  interosseous  ligament. 
The  three  facets  for  articulation  with  the  three  metatarsal  bones  are  continuous 
with  one  another;  those  for  articulation  with  the  second  cuneiform  and  navicular 
are  also  continuous,  but  that  for  articulation  with  the  cuboid  is  usually  separate. 
The  dorsal  surface  is  of  an  oblong  form,  its  postero-lateral  angle  being  prolonged 
backward.  The  plantar  surface  is  a  rounded  margin,  and  serves  for  the  attachment 
of  part  of  the  tendon  of  the  Tibialis  posterior,  part  of  the  Flexor  hallucis  brevis, 
and  ligaments. 


Articulations. — ^The  third  cuneiform  articulates  with  six  bones: 
form,  cuboid,  and  second,  third,  and  fourth  metatarsals. 


the  navicular,  second  cunei- 


For  navicular    For  2nd  cuneiform 


For  cuboid 


Fig.  282. — The  left  third  cuneiform, 
view. 


For  2nd 

metatarsal 


Postero-medial 


Fig. 


Forird 
metatarsal 

283. — The  third  left  cuneiform, 
lateral  view. 


Antero- 


The  Metatarsus. 

The  metatarsus  consists  of  five  bones  which  are  numbered  from  the  medial 
side  {ossa  metatarsalia  I.-V.);  each  presents  for  examination  a  body  and  two 
extremities. 

Common  Characteristics  of  the  Metatarsal  Bones. — The  body  is  prismoid  in 
form,  tapers  gradually  from  the  tarsal  to  the  phalangeal  extremity,  and  is  curved 
longitudinally,  so  as  to  be  concave  below,  slightly  convex  above.  The  base  or 
posterior  extremity  is  wedge-shaped,  articulating  proximally  with  the  tarsal  bones, 
and  by  its  sides  with  the  contiguous  metatarsal  bones:  its  dorsal  and  plantar 
surfaces  are  rough  for  the  attachment  of  ligaments.  The  head  or  anterior  extremity 
presents  a  convex  articular  surface,  oblong  from  above  downward,  and  extend- 
ing farther  backward  below  than  above.  Its  sides  are  flattened,  and  on  each  is  a 
depression,  surmounted  by  a  tubercle,  for  ligamentous  attachment.  Its  plantar 
surface  is  grooved  antero-posteriorly  for  the  passage  of  the  Flexor  tendons,  and 
marked  on  either  side  by  an  articular  eminence  continuous  with  the  terminal 
articular  surface. 

Characteristics  of  the  Individual  Metatarsal  Bones.  —  The  First  Metatarsal 
Bone  (os  metatarsale  I;  metatarsal  bone  of  the  great  toe)  (Fig.  284). — The  first 
metatarsal  bone  is  remarkable  for  its  great  thickness,  and  is  the  shortest  of 
the  metatarsal  bones.  The  body  is  strong,  and  of  well-marked  prismoid  form. 
The  base  presents,  as  a  rule,  no  articular  facets  on  its  sides,  but  occasionally 
on  the  lateral  side  there  is  an  oval  facet,  by  which  it  articulates  with  the  second 
metatarsal.  Its  proximal  articular  surface  is  of  large  size  and  kidney-shaped;  its 
circumference  is  grooved,  for  the  tarsometatarsal  ligaments,  and  medially  gives 
insertion  to  part  of  the  tendon  of  the  Tibialis  anterior;  its  plantar  angle  presents 
a  rough  oval  prominence  for  the  insertion  of  the  tendon  of  the  Peronseus  longus. 
The  head  is  large;  on  its  plantar  surface  are  two  grooved  facets,  on  which  glide 
sesamoid  bones;  the  facets  are  separated  by  a  smooth  elevation. 


THE  METATARSUS 


273 


The  Second  Metatarsal  Bone  {os  metatarsale  II)  (Fig.  285). — The  second  meta- 
tarsal bone  is  the  longest  of  the  metatarsal  bones,  being  prolonged  backward 


For  sesamoid  bones 


For  1st  For  PeroruBfua 

CU7ieiform  Umgus 

Fig.  284.— The  first  metatarsal.     (Left.) 


Fm  1st 

cuneiform      For  2nd  For  'Srd 

cuneiform  cuneiform 

Fig.  285. — The  second  metatarsal.     (Left.) 


For  2nd 

metatarsal  I    For  2nd 

For       meta- 
3rd        tarsal 
cuneiform 


For  Ath 
metatarsal 


Fig.  286.— The  third  metatarsal.     (Left.) 


For  Srd 
metatarsal 


For  cuboid 

For  3rd  cuneiform  For  5th  metatarsal 

Fig.  287. — The  fourth  metatarsal.     (Left.) 


into  the  recess  formed  by  the  three  cuneiform  bones.  Its  base  is  broad  above, 
narrow  and  rough  below.  It  presents  four  articular  surfaces:  one  behind,  of  a 
triangular  form,  for  articulation  with  the  second  cuneiform;  one  at  the  upper  part 

IS 


274 


OSTEOLOGY 


I 


of  its  medial  surface,  for  articulation  with  the  first  cuneiform;  and  two  on  its  lat(;ral 
surface,  an  upper  and  lower,  separated  by  a  rough  non-articular  interval.  Each 
of  these  lateral  articular  surfaces  is  divided  into  two  by  a  vertical  ridge;  the  two 
anterior  facets  articulate  with  the  third  metatarsal;  the  two  posterior  (sometiraes 
continuous)  with  the  third  cuneiform.  A  fifth  facet  is  occasionally  present  for 
articulation  with  the  first  metatarsal;  it  is  oval  in  shape,  and  is  situated  on  the 
medial  side  of  the  body  near  the  base. 

The  Third  Metatarsal  Bone  {os  metatarsale  III)  (Fig.  286). — The  third  meta- 
tarsal bone  articulates  proximally,  by  means  of  a  triangular  smooth  surface, 
with  the  third  cuneiform;  medially,  by  two  facets,  with  the  second  metatarsal; 
and  laterally,  by  a  single  facet,  with  the  fourth  metatarsal.  This  last  facet  is 
situated  at  the  dorsal  angle  of  the  base. 


iir 


P. 

For  Uk 
metatarsal        For  cuboid        Tuberosity 

Fia.  288.— The  fifth  metatarsal.     (Left.) 

The  Fourth  Metatarsal  Bone  {os  metatarsale  IV)  (Fig.  2<S7). — The  fourth  meta- 
tarsal bone  is  smaller  in  size  than  the  preceding;  its  base  presents  an  oblique 
quadrilateral  surface  for  articulation  with  the  cuboid ;  a  smooth  facet  on  the  medial 
side,  divided  by  a  ridge  into  an  anterior  portion  for  articulation  witli  the  third 
metatarsal,  and  a  posterior  portion  for  articulation  with  the  third  cuneiform;  on 
the  lateral  side  a  single  facet,  for  articulation  with  the  fifth  metatarsal. 

The  Fifth  Metatarsal  Bone  {os  metatarsale  V)  (Fig.  288). — The  fifth  metatarsal 
bone  is  recognized  by  a  rough  eminence,  the  tuberosity,  on  the  lateral  side  of  its 
base.  The  base  articulates  behind,  by  a  triangular  surface  cut  obliquely  in  a  trans- 
verse direction,  with  the  cuboid;  and  medially,  wuth  the  fourth  metatarsal.  On 
the  medial  part  of  its  dorsal  surface  is  inserted  the  tendon  of  the  Peron?eus  tertius 
and  on  the  dorsal  surface  of  the  tuberosity  that  of  the  Peronseus  brevis.  A  strong 
band  of  the  plantar  aponeurosis  connects  the  projecting  part  of  the  tuberosity 
with  the  lateral  process  of  the  tuberosity  of  the  calcaneus.  The  plantar  surface 
of  the  base  is  grooved  for  the  tendon  of  the  Abductor  digiti  quinti,  and  gives  origin 
to  the  Flexor  digiti  quinti  brevis. 

Articulations. — The  base  of  each  metatarsal  bone  articulates  with  one  or  more  of  the  tarsal 
bones,  and  the  head  with  one  of  the  first  row  of  phalanges.  The  first  metatarsal  articulates  with 
the  first  cuneiform,  the  second  with  all  three  cuneiforms,  the  third  with  the  third  cuneiform,  the 
fourth  with  the  third  cuneiform  and  the  cuboid,  and  the  fifth  with  the  cuboid. 


THE  PHALANGESOF  THE  FOOT 


The  Phalanges  of  the  Foot  (Phalanges  Digitorum  Pedis). 


275 


The  phalanges  of  the  foot  correspond,  in  number  and  general  arrangement, 
with  those  of  the  hand;  there  are  two  in  the  great  toe,  and  three  in  each  of  the 
other  toes.  They  differ  from  them,  however,  in  their  size,  the  bodies  being  much 
reduced  in  length,  and,  especially  in  the  first  row,  laterally  compressed. 

First  Row. — The  body  of  each  is  compressed  from  side  to  side,  convex  above, 
concave  below.  The  base  is  concave;  and  the  head  presents  a  trochlear  surface 
for  articulation  with  the  second  phalanx. 

Second  Row. — The  phalanges  of  the  second  row  are  remarkably  small  and  short, 
but  rather  broader  than  those  of  the  first  row. 

The  ungual  phalanges,  in  form,  resemble  those  of  the  fingers;  but  they  are  smaller 
and  are  flattened  from  above  downward ;  each  presents  a  broad  base  for  articula- 
tion with  the  corresponding  bone  of  the  second  row,  and  an  expanded  distal 
extremity  for  the  support  of  the  nail  and  end  of  the  toe. 


One  center  for  each  bone, 
except  calcaneus 


OUTER  FOtJE  METATARSALS. 

Tv)o  centers  for  each  hone  . 
One  for  body 
One  for  Jiead 


PHALANQES. 

Two  centers  for  each  bone  : 
One  for  body 
One  for  metatarsal 
extremity 


Appears  10th  year; 
unites  after  puberty 


Appears  Srd  year 
}  Unite  18th-20th  year 

~  Apjxars  1th  week 


Unite  18-20  j/r.  ^ 
Apps.  Srd  yr. 

App.  ith  yr^ 
Unite  17-18  yr. 

App.  2-4  mo.  _ 


App.  6-7th  yr. 
Unite  17-18  yr.  J 

App.  2-4  mo. 

App.  6th  yr. 
Unite  17-18  yr.  | 

App,  7th  wk, 

FiQ.  289. — Plan  of  ossification  of  the  foot. 


iculations. — In  the  second,  third,  fourth,  and  fifth  toes  the  phalanges  of  the  first  row  articu- 
late behind  with  the  metatarsal  bones,  and  in  front  with  the  second  phalanges,  which  in  their 
turn  articulate  with  the  first  and  third:    the  ungual  phalanges  articulate  with  the  second. 

Ossification  of  the  Bones  of  the  Foot  (Fig.  289). — The  tarsal  bones  are  each  ossified  from  a 
single  center,  excepting  the  calcaneus,  which  has  an  epiphysis  for  its  posterior  extremity.  The 
centers  make  their  appearance  in  the  following  order:    calcaneus  at  the  sixth  month  of  fetal  life; 


276 


OSTEOLOGY 


talus,  about  the  seventh  month;  cuboid,  at  the  ninth  nronth;  third  cuneiform,  during  the  first 
year;  first  cuneiform,  in  the  third  year;  second  cuneiform  and  navicular,  in  the  fourth  year. 
The  epiphysis  for  the  posterior  extremity  of  the  calcaneus  appears  at  the  tenth  year,  and  unites 
with  the  rest  of  the  bone  soon  after  puberty.  The  posterior  process  of  the  talus  is  sometimt^a 
ossified  from  a  separate  center,  and  may  remain  distinct  from  the  main  mass  of  the  bone,  when 
it  is  named  the  os  trigonum. 

The  metatarsal  bones  are  each  ossified  from  two  centers:  one  for  the  body,  and  one  for  the 
head,  of  the  second,  third,  fourth,  and  fifth  metatarsals;  one  for  the  body,  and  one  for  the  base, 
of  the  first  metatarsal.^  Ossification  commences  in  the  center  of  the  body  about  the  ninth  week, 
and  extends  toward  either  extremity.  The  center  for  the  base  of  the  first  metatarsal  appeai-s 
about  the  third  year;  the  centers  for  the  heads  of  the  other  bones  between  the  fifth  and  eighth 
years;  they  join  the  bodies  between  the  eighteenth  and  twentieth  years. 

The  phalanges  are  each  ossified  from  two  centers:  one  for  the  body,  and  one  for  the  base. 
The  center  for  the  body  appears  about  the  tenth  week,  that  for  the  base  between  the  fourth  and 
tenth  years;  it  joins  the  body  about  the  eighteenth  year. 

Comparison  of  the  Bones  of  the  Hand  and  Foot. 

The  hand  and  foot  are  constructed  on  somewhat  similar  principles,  each  con- 
sisting of  a  proximal  part,  the  carpus  or  the  tarsus,  a  middle  portion,  the  meta- 
carpus, or  the  metatarsus,  and  a  terminal  portion,  the  phalanges.  The  proximal 
part  consists  of  a  series  of  more  or  less  cubical  bones  which  allow  a  slight  amount 
of  gliding  on  one  another  and  are  chiefly  concerned  in  distributing  forces  transmitted 
to  or  from  the  bones  of  the  arm  or  leg.  The  middle  part  is  made  up  of  slightly 
movable  long  bones  which  assist  the  carpus  or  tarsus  in  distributing  forces  and 
also  give  greater  breadth  for  the  reception  of  such  forces.  The  separation  of  the 
individual  bones  from  one  another  allows  of  the  attachments  of  the  Interossei  and 
protects  the  dorsi-palmar  and  dorsi-plantar  vascular  anastomoses.  The  terminal 
portion  is  the  most  movable,  and  its  separate  elements  enjoy  a  varied  range  of 
movements,  the  chief  of  which  are  flexion  and  extension. 


Fig.  290. — Skeleton  of  foot.     Medial  aspect. 

The  function  of  the  hand  and  foot  are,  however,  very  different,  and  the  general 
similarity  between  them  is  greatly  modified  to  meet  these  requirements.  Thus  the 
foot  forms  a  firm  basis  of  support  for  the  body  in  the  erect  posture,  and  is  there- 
fore more  solidly  built  up  and  its  component  parts  are  less  movable  on  each  other 
than  those  of  the  hand.  In  the  case  of  the  phalanges  the  difference  is  readily 
noticeable;  those  of  the  foot  are  smaller  and  their  movements  are  more  limited 
than  those  of  the  hand.  Very  much  more  marked  is  the  difference  between  the 
metacarpal  bone  of  the  thumb  and  the  metatarsal  bone  of  the  great  toe.  The  meta- 
carpal bone  of  the  thumb  is  constructed  to  permit  of  great  mobility,  is  directed  at 
an  acute  angle  from  that  of  the  index  finger,  and  is  capable  of  a  considerable  range 

'  As  was  noted  in  the  first  metacarpal  (see  footnote,  page  231),  so  in  the  first  metatarsal,  there  is  often  a  second 
epiphysis  for  its  head. 


THESM 


277 


of  movements  at  its  articulation  with  the  carpus.  The  metatarsal  bone  of  the 
great  toe  assists  in  supporting  the  weigh  fc  of  the  body,  is  constructed  with  great 
sohdity,  lies  parallel  with  the  other  metatarsals,  and  has  a  very  limited  degree  of 
mobility.  The  carpus  is  small  in  proportion  to  the  rest  of  the  hand,  is  placed 
in  line  with  the  forearm,  and  forms  a  transverse  arch,  the  concavity  of  which 
constitutes  a  bed  for  the  Flexor  tendons  and  the  palmar  vessels  and  nerves.  The 
tarsus  forms  a  considerable  part  of  the  foot,  and  is  placed  at  right  angles  to  the 
leg,  a  position  w^hich  is  almost  peculiar  to  man,  and  has  relation  to  his  erect  pos- 
ture. In  order  to  allow  of  their  supporting  the  weight  of  the  body  with  the  least 
expenditure  of  material  the  tarsus  and  a  part  of  the  metatarsus  are  constructed 
in  a  series  of  arches  (Figs.  290,  291),  the  disposition  of  which  will  be  considered 
after  the  articulations  of  the  foot  have  been  described. 


Fig.  291. — Skeleton  of  foot.     Lateral  aspect. 

The  Sesamoid  Bones  (Ossa  Sesamoidea). 

Sesamoid  bones  are  small  more  or  less  rounded  masses  embedded  in  certain 
tendons  and  usually  related  to  joint  surfaces.  Their  functions  probably  are  to 
modify  pressure,  to  diminish  friction,  and  occasionally  to  alter  the  direction  of  a 
muscle  pull.  That  they  are  not  developed  to  meet  certain  physical  requirements 
in  the  adult  is  evidenced  by  the  fact  that  they  are  present  as  cartilaginous  nodules 
in  the  fetus,  and  in  greater  numbers  than  in  the  adult.  They  must  be  regarded, 
according  to  Thilenius,  as  integral  parts  of  the  skeleton  phylogenetically  inherited.* 
Physical  necessities  probably  come  into  play  in  selecting  and  in  regulating  the 
degree  of  development  of  the  original  cartilaginous  nodules.  Nevertheless,  irreg- 
ular nodules  of  bone  may  appear  as  the  result  of  intermittent  pressure  in  certain 
regions,  e.  g.,  the  "rider's  bone,"  which  is  occasionally  developed  in  the  Adductor 
muscles  of  the  thigh. 

Sesamoid  bones  are  invested  by  the  fibrous  tissue  of  the  tendons,  except  on  the 
surfaces  in  contact  with  the  parts  over  which  they  glide,  where  they  present 
smooth  articular  facets. 

In  the  upper  extremity  the  sesamoid  bones  of  the  joints  are  found  only  on  the 
palmar  surface  of  the  hand.  Two,  of  which  the  medial  is  the  the  larger,  are  constant 
at  the  metacarpophalangeal  joint  of  the  thumb;  one  is  frequently  present  in  the 
corresponding  joint  of  the  little  finger,  and  one  (or  two)  in  the  same  joint  of  the 
index  finger.  Sesamoid  bones  are  also  found  occasionally  at  the  metacarpopha- 
langeal joints  of  the  middle  and  ring  fingers,  at  the  interphalangeal  joint  of  the 
thumb  and  at  the  distal  interphalangeal  joint  of  the  index  finger. 

In  the  lower  extremity  the  largest  sesamoid  bone  of  the  joints  is  the  patella, 
developed  in  the  tendon  of  the  Quadriceps  femoris.  On  the  plantar  aspect  of  the 
foot,  two,  of  which  the  medial  is  the  larger,  are  always  present  at  the  metatar- 

»  Morpholog.  Arbeiten,  1906,  v,  309. 


18 


OSTEOLOGY 


sophalangeal  joint  of  the  great  toe;  one  sometimes  at  the  metatarsophalangeal 
joints  of  the  second  and  fifth  toes,  one  occasionally  at  the  corresponding  joint  of 
the  third  and  fourth  toes,  and  one  at  the  interphalangeal  joint  of  the  great  toe. 

Sesamoid  bones  apart  from  joints  are  seldom  found  in  the  tendons  of  the  upp(;r 
limb;  one  is  sometimes  seen  in  the  tendon  of  the  Biceps  brachii  opposite  the  radial 
tuberosity.  They  are,  however,  present  in  several  of  the  tendons  of  the  lower 
limb,  viz.,  one  in  the  tendon  of  the  Peronseus  longus,  where  it  glides  on  the  cuboid; 
one,  appearing  late  in  life,  in  the  tendon  of  the  Tibialis  anterior,  opposite  the  smooth 
facet  of  the  first  cuneiform  bone;  one  in  the  tendon  of  the  Tibialis  posterior,  oppo- 
site the  medial  side  of  the  head  of  the  talus;  one  in  the  lateral  head  of  the  Gastroo 
nemius,  behind  the  lateral  condyle  of  the  femur;  and  one  in  the  tendon  of  the  Psoas 
major,  where  it  glides  over  the  pubis.  Sesamoid  bones  are  found  occasionally 
in  the  tendon  of  the  Glutseus  maximus,  as  it  passes  over  the  greater  trochanter, 
and  in  the  tendons  which  wind  around  the  medial  and  lateral  malleoli. 


SYNDESMOLOGY. 


THE  bones  of  the  skeleton  are  joined  to  one  another  at  different  parts  of  their 
surfaces,  and  such  connections  are  termed  Joints  or  Articulations,  Where 
the  joints  are  immovable,  as  in  the  articulations  between  practically  all  the  bones 
of  the  skull,  the  adjacent  margins  of  the  bones  are  almost  in  contact,  being  separated 
merely  by  a  thin  layer  of  fibrous  membrane,  named  the  sutural  ligament.  In  certain 
regions  at  the  base  of  the  skull  this  fibrous  membrane  is  replaced  by  a  layer  of  car- 
tilage. Where  slight  movement  combined  with  great  strength  is  required,  the  osseous 
surfaces  are  united  by  tough  and  elastic  fibrocartilages,  as  in  the  joints  between  the 
vertebral  bodies,  and  in  the  interpubic  articulation.  In  the  freely  movable  joints 
the  surfaces  are  completely  separated;  the  bones  forming  the  articulation  are  ex- 
panded for  greater  convenience  of  mutual  connection,  covered  by  cartilage  and 
enveloped  by  capsules  of  fibrous  tissue.  The  cells  lining  the  interior  of  the  fibrous 
capsule  form  an  imperfect  membrane— the  sjmovial  membrane — which  secretes 
a  lubricating  fluid.  The  joints  are  strengthened  by  strong  fibrous  bands  called 
ligaments,  which  extend  between  the  bones  forming  the  joint. 

Bone. — Bone  constitutes  the  fundamental  element  of  all  the  joints.  In  the 
long  bones,  the  extremities  are  the  parts  which  form  the  articulations;  they  are 
generally  somewhat  enlarged;  and  consist  of  spongy  cancellous  tissue  with  a  thin 
coating  of  compact  substance.  In  the  flat  bones,  the  articulations  usually  take 
place  at  the  edges;  and  in  the  short  bones  at  various  parts  of  their  surfaces.  The 
layer  of  compact  bone  which  forms  the  joint  surface,  and  to  which  the  articular 
cartilage  is  attached,  is  called  the  articular  lamella.  It  differs  from  ordinary 
bone  tissue  in  that  it  contains  no  Haversian  canals,  and  its  lacunae  are  larger 
and  have  no  canaliculi.  The  vessels  of  the  cancellous  tissue,  as  they  approach 
the  articular  lamella,  turn  back  in  loops,  and  do  not  perforate  it;  this  layer  is  con- 
sequently denser  and  firmer  than  ordinary  bone,  and  is  evidently  designed  to  form 
an  unyielding  support  for  the  articular  cartilage. 

Cartilage. — Cartilage  is  a  non-vascular  structure  which  is  found  in  various 
parts  of  the  body — in  adult  life  chiefly  in  the  joints,  in  the  parietes  of  the  thorax, 
and  in  various  tubes,  such  as  the  trachea  and  bronchi,  nose,  and  ears,  which  require 
to  be  kept  permanently  open.  In  the  fetus,  at  an  early  period,  the  greater  part 
of  the  skeleton  is  cartilaginous;  as  this  cartilage  is  afterward  replaced  by  bone, 
it  is  called  temporary,  in  contradistinction  to  that  which  remains  unossified  during 
the  whole  of  life,  and  is  called  permanent. 

Cartilage  is  divided,  according  to  its  minute  structure,  into  hyaline  cartjlage, 
white  fibrocartilage,  and  yellow  or  elastic  fibrocartilage. 

Hyaline  Cartilage. — Hyaline  cartilage  consists  of  a  gristly  mass  of  a  firm  consist- 
ence, but  of  considerable  elasticity  and  pearly  bluish  color.  Except  where  it  coats 
the  articular  ends  of  bones,  it  is  covered  externally  by  a  fibrous  membrane,  the 
perichondrium,  from  the  vessels  of  which  it  imbibes  its  nutritive  fluids,  being  itself 
destitute  of  bloodvessels.  It  contains  no  nerves.  Its  intimate  structure  is  very 
simple.  If  a  thin  slice  be  examined  under  the  microscope,  it  will  be  found  to  consist 
of  cells  of  a  rounded  or  bluntly  angular  form,  lying  in  groups  of  two  or  more  in 
a  granular  or  almost  homogeneous  matrix  (Fig.  292).  The  cells,  when  arranged 
in  groups  of  two  or  more,  have  generally  straight  outlines  where  they  are  in  contact 

(279) 


280 


SYNDESMOLOGY 


with  each  other,  and  in  the  rest  of  their  circumference  are  rounded.  They  con- 
sist of  clear  translucent  protoplasm  in  which  fine  interlacing  filaments  and  minute 
granules  are  sometimes  present;  imbedded  in  this  are  one  or  two  round  nuchi, 
having  the  usual  intranuclear  network.  The  cells  are  contained  in  cavities  in 
the  matrix,  called  cartilage  lacunae ;  around  these  the  matrix  is  arranged  in  co)i- 
centric  lines,  as  if  it  had  been  formed  in  successive  portions  around  the  cartilage 
cells.     This  constitutes  the  so-called  capsule  of  the  space.    Each  lacuna  is  generally 

occupied  by  a  single  cell,  but  dur- 
ing the  division  of  the  cells  it  may 
contain  two,  four,  or  eight  cells. 

The  matrix  is  transparent  and 
apparently  without  structure,  or 
else  presents  a  dimly  granular  ap- 
pearance, like  ground  glass.  Some 
observers  have  shown  that  the 
matrix  of  hyaline  cartilage,  and 
especially  of  the  articular  variety, 
after  prolonged  maceration,  can 
be  broken  up  into  fine  fibrils. 
These  fibrils  are  probably  of  the  same  nature,  chemically,  as  the  w^hite  fibers 
of  connective  tissue.  It  is  believed  by  some  histologists  that  the  matrix  is  per- 
meated by  a  number  of  fine  channels,  which  connect  the  lacunae  with  each  other, 
and  that  these  canals  communicate  with  the  lymphatics  of  the  perichondrium, 
and  thus  the  structure  is  permeated  by  a  current  of  nutrient  fluid. 

Articular  cartilage,  costal  cartilage,  and  temporary  cartilage  are  all  of  the  hyaline 
variety.  They  present  difi^erences  in  the  size,  shape,  and  arrangement  of  their 
cells. 


Fig.  292. — Human  cartilage  cells  from  the  cricoid  cartilage. 
X  350 


"J^g|  Superficial  fiattened  cells 


Vertical  rows  of  cells 


%3t'. v!^"'*'!-' "."•'•"•?h^^^  f  Colcifi^ 


matrix 


Bone 


Fig.  293. — Vertical  section  of  articular  cartUage. 


Fig.  294. — Costal  cartilage  from  a  man,  aged 
seventy-six  years,  showing  the  development  of 
fibrous  structure  in  the  matrix.  In  several  por- 
tions of  the  specimen  two  or  three  generations  of 
cells  are  seen  enclosed  in  a  parent  cell  wall. 
Highly  magnified. 


In  Articular  Cartilage  (Fig.  293),  which  shows  no  tendency  to  ossification,  the 
matrix  is  finely  granular;  the  cells  and  nuclei  are  small,  and  are  disposed  parallel 
to  the  surface  in  the  superficial  part,  while  nearer  to  the  bone  they  are  arranged  in 
vertical  rows.  Articular  cartilages  have  a  tendency  to  split  in  a  vertical  direction; 
in  disease  this  tendency  becomes  very  manifest.  The  free  surface  of  articular 
cartilage,  where  it  is  exposed  to  friction,  is  not  covered  by  perichondrium,  although 
a  layer  of  connective  tissue  continuous  with  that  of  the  synovial  membrane  can  be 


A 


I 


CARTILAGE 


281 


traced  in  the  adult  over  a  small  part  of  its  circumference,  and  here  the  cartilage 
cells  are  more  or  less  branched  and  pass  insensibly  into  the  branched  connective 
tissue  corpuscles  of  the  synovial  membrane.  Articular  cartilage  forms  a  thin 
incrustation  upon  the  joint  surfaces  of  the  bones,  and  its  elasticity  enables  it  to 
break  the  force  of  concussions,  while  its  smoothness  affords  ease  and  freedom  of 
movement.  It  varies  in  thickness  according  to  the  shape  of  the  articular  surface 
on  which  it  lies;  where  this  is  convex  the  cartilage  is  thickest  at  the  center,  the 
reverse  being  the  case  on  concave  articular  surfaces.  It  appears  to  derive  its 
nutriment  partly  from  the  vessels  of  the  neighboring  synovial  membrane  and 
partly  from  those  of  the  bone  upon  which  it  is  implanted.  Toynbee  has  shown 
that  the  minute  vessels  of  the  cancellous  tissue  as  they  approach  the  articular 
lamella  dilate  and  form  arches,  and  then  return  into  the  substance  of  the  bone. 

In  Costal  Cartilage  the  cells  and  nuclei  are  large,  and  the  matrix  has  a  tendency 
to  fibrous  striation,  especially  in  old  age  (Fig.  294).  In  the  thickest  parts  of  the 
costal  cartilages  a  few  large  vascular  channels  may  be  detected.  This  appears, 
at  first  sight,  to  be  an  exception  to  the  statement  that  cartilage  is  a  non-vascular 
tissue,  but  is  not  so  really,  for  the  vessels  give  no  branches  to  the  cartilage  sub- 
stance itself,  and  the  channels  may  rather  be  looked  upon  as  involutions  of  the 
])erichondrium.  The  xiphoid  process  and  the  cartilages  of  the  nose,  larynx,  and 
trachea  (except  the  epiglottis  and  corniculate  cartilages  of  the  larynx,  which  are 
(jomposed  of  elastic  fibrocartilage)  resemble  the  costal  cartilages  in  microscopic 
(characteristics.  The  arytenoid  cartilage  of  the  larynx  shows  a  transition  from 
jiyaline  cartilage  at  its  base  to  elastic  cartilage  at  the  apex. 

The  hyaline  cartilages,  especially  in  adult  and  advanced  life,  are  prone  to  calcify 
— that  is  to  say,  to  have  their  matrix  permeated  by  calcium  salts  without  any 
appearance  of  true  bone.  The  process  of  calcification  occurs  frequently,  in  such 
cartilages  as  those  of  the  trachea  and  in  the  costal  cartilages,  where  it  may  be 
succeeded  by  conversion  into  true  bone. 

White  Fibrocartilage. — ^White  fibrocartilage  consists  of  a  mixture  of  white  fibrous 
tissue  and  cartilaginous  tissue  in  various  proportions;  to  the  former  of  these  con' 
stituents  it  owes  its  flexibility  and 
toughness,  and  to  the  latter  its 
elasticity.  When  examined  under 
the  microscope  it  is  found  to  be 
made  up  of  fibrous  connective 
tissue  arranged  in  bundles,  with 
cartilage  cells  between  the  bundles; 
the  cells  to  a  certain  extent  re- 
semble tendon  cells,  but  may  be 
distinguished  from  them  by  being 
surrounded  by  a  concentrically 
striated  area  of  cartilage  matrix 
and  by  being  less  flattened  (Fig. 
295).  The  white  fibrocartilages  ad- 
mit of  arrangement  into  four 
groups — ^interarticular,  connecting, 
circumferential,  and  stratiform. 

1.  The  Interarticular  Fibrocartilages  {menisci)  are  flattened  fibrocartilaginous 
plates,  of  a  round,  oval,  triangular,  or  sickle-like  form,  interposed  between  the 
articular  cartilages  of  certain  joints.  They  are  free  on  both  surfaces,  usually 
thinner  toward  the  center  than  at  the  circumference,  and  held  in  position  by  the 
attachment  of  their  margins  and  extremities  to  the  surrounding  ligaments.  The 
synovial  membranes  of  the  joints  are  prolonged  over  them.  They  are  found 
in  the  temporomandibular,  sternoclavicular,  acromioclavicular,  wrist,  and  knee 


Fig.  295. — White  fibrocartilage  from  an  intervertebral 
fibrocartilage. 


I 


282  SYNDESMOLOGY 

joints — i.  e.,  in  those  joints  which  are  most  exposed  to  violent  concussion  and  I 
subject  to  frequent  movement.  Their  uses  are  to  obHterate  the  intervals  between 
opposed  surfaces  in  their  various  motions;  to  increase  the  depths  of  the  articular 
surfaces  and  give  ease  to  the  gliding  movements;  to  moderate  the  effects  of  great 
pressure  and  deaden  the  intensity  of  the  shocks  to  which  the  parts  may  be  sub- 
jected. Humphry  has  pointed  out  that  these  interarticular  fibrocartilages  serve 
an  important  purpose  in  increasing  the  varieties  of  movement  in  a  joint.  Thus 
in  the  knee  joint  there  are  two  kinds  of  motion,  viz.,  angular  movement  and  rota- 
tion, although  it  is  a  hinge  joint,  in  which,  as  a  rule,  only  one  variety  of  motion 
is  permitted ;  the  former  movement  takes  place  between  the  condyles  of  the  femur 
and  the  interarticular  cartilages,  the  latter  between  the  cartilages  and  the  head 
of  the  tibia.  So,  also,  in  the  temporomandibular  joint,  the  movements  of  opening 
and  shutting  the  mouth  take  place  between  the  fibrocartilage  and  the  mandible, 
the  grinding  movement  between  the  mandibular  fossa  and  the  fibrocartilage,  the 
latter  moving  with  the  mandible. 

2.  The  Connecting  Fibrocartilages  are  interposed  between  the  bony  surfaces  of 
those  joints  which  admit  of  only  slight  mobility,  as  between  the  bodies  of  the 
vertebrae.  They  form  disks  which  are  closely  adherent  to  the  opposed  surfaces. 
Each  disk  is  composed  of  concentric  rings  of  fibrous  tissue,  'with  cartilaginous 
laminae  interposed,  the  former  tissue  predominating  toward  the  circumference, 
the  latter  toward  the  center. 

3.  The  Circumferential  Fibrocartilages  consist  of  rims  of  fibrocartilage,  which 
surround  the  margins  of  some  of  the  articular  cavities,  e.  g.,  the  glenoidal  labrum 
of  the  hip,  and  of  the  shoulder;  they  serve  to  deepen  the  articular  cavities  and  to 
protect  their  edges. 

4.  The  Stratiform  Fibrocartilages  are  those  which  form  a  thin  coating  to  osseous 
grooves  through  which  the  tendons  of  certain  muscles  glide.  Small  masses  of  fibro- 
cartilage are  also  developed  in  the  tendons  of  some  muscles,  where  they  glide 
over  bones,  as  in  the  tendons  of  the  Peronseus  longus  and  Tibialis  posterior. 

The  distinguishing  feature  of  cartilage  chemically  is  that  it  yields  on  boiling  a 
substance  called  chondrin,  very  similar  to  gelatin,  but  differing  from  it  in  several 
of  its  reactions.  It  is  now  believed  that  chondrin  is  not  a  simple  body,  but  a 
mixture  of  gelatin  with  mucinoid  substances,  chief  among  which,  perhaps,  is  a 
compound  termed  chondro-mucoid. 

Ligaments.— Ligaments  are  composed  mainly  of  bundles  of  white  fibrous  tissue 
placed  parallel  with,  or  closely  interlaced  with  one  another,  and  present  a  white, 
shining,  silvery  appearance.  They  are  pliant  and  flexible,  so  as  to  allow  perfect 
freedom  of  movement,  but  strong,  tough,  and  inextensible,  so  as  not  to  yield 
readily  to  applied  force.  Some  ligaments  consist  entirely  of  yellow  elastic  tissue, 
as  the  ligamenta  flava  which  connect  together  the  laminse  of  adjacent  vertebrae, 
and  the  ligamentum  nuchse  in  the  lower  animals.  In  these  cases  the  elasticity  of 
the  ligament  is  intended  to  act  as  a  substitute  for  muscular  power. 

The  Articular  Capsules. — The  articular  capsules  form  complete  envelopes  for  the 
freely  movable  joints.  Each  capsule  consists  of  two  strata — an  external  {stratum 
fihrosum)  composed  of  white  fibrous  tissue,  and  an  internal  {stratmn  synoviale) 
which  is  a  secreting  layer,  and  is  usually  described  separately  as  the  synovial 
membrane. 

The  fibrous  capsule  is  attached  to  the  whole  circumference  of  the  articular  end 
of  each  bone  entering  into  the  joint,  and  thus  entirely  surrounds  the  articulation. 

The  S3movial  membrane  invests  the  inner  surface  of  the  fibrous  capsule,  and  is 
reflected  over  any  tendons  passing  through  the  joint  cavity,  as  the  tendon  of  the 
Popliteus  in  the  knee,  and  the  tendon  of  the  Biceps  brachii  in  the  shoulder.  It  is 
composed  of  a  thin,  delicate,  connective  tissue,  with  branched  connective-tissue 
-corpuscles.    Its  secretion  is  thick,  viscid,  and  glairy,  like  the  white  of  an  egg,  and 


I 


DEVELOPMENT  OF  THE  JOIl 


I 


is  hence  termed  synovia.  In  the  fetus  this  membrane  is  said,  by  Toynbee,  to  be 
(3ontinued  over  the  surfaces  of  the  cartilages ;  but  in  the  adult  such  a  continuation 
is  wanting,  excepting  at  the  circumference  of  the  cartilage,  upon  which  it  encroaches 
for  a  short  distance  and  to  which  it  is  firmly  attached.  In  some  of  the  joints  the 
synovial  membrane  is  thrown  into  folds  which  pass  across  the  cavity;  they  are 
especially  distinct  in  the  knee.  In  other  joints  there  are  flattened  folds,  subdivided 
at  their  margins  into  fringe-like  processes  which  contain  convoluted  vessels. 
These  folds  generally  project  from  the  synovial  membrane  near  the  margin  of  the 
cartilage,  and  lie  flat  upon  its  surface.  They  consist  of  connective  tissue,  covered 
with  endothelium,  and  contain  fat  cells  in  variable  quantities,  and,  more  rarely, 
isolated  cartilage  cells ;  the  larger  folds  often  contain  considerable  quantities  of  fat. 

Closely  associated  with  synovial  membrane,  and  therefore  conveniently  described 
in  this  section,  are  the  mucous  sheaths  of  tendons  and  the  mucous  bursae. 

Mucous  sheaths  {vaginoe  viucoscf)  serve  to  facilitate  the  gliding  of  tendons  in 
fibroosseous  canals.  Each  sheath  is  arranged  in  the  form  of  an  elongated  closed 
sac,  one  layer  of  which  adheres  to  the  wall  of  the  canal,  and  the  other  is  reflected 
upon  the  surface  of  the  enclosed  tendon.  These  sheaths  are  chiefly  found  surround- 
ing the  tendons  of  the  Flexor  and  Extensor  muscles  of  the  fingers  and  toes  as  they 
pass  through  fibroosseous  canals  in  or  near  the  hand  and  foot. 

Suisse  mucosae  are  interposed  between  surfaces  which  glide  upon  each  other. 
They  consist  of  closed  sacs  containing  a  minute  quantity  of  clear  viscid  fluid,  and 
may  be  grouped,  according  to  their  situations,  under  the  headings  subcutaneous, 
submuscular,  subfacial,  and  subtendinous. 

I  DEVELOPMENT   OF   THE   JOINTS. 

The  mesoderm  from  which  the  different  parts  of  the  skeleton  are  formed  shows 
at  first  no  differentiation  into  masses  corresponding  with  the  individual  bones. 
Thus  continuous  cores  of  mesoderm  form  the  axes  of  the  limb-buds  and  a  continu- 
ous column  of  mesoderm  the  future  vertebral  column.  The  first  indications  of  the 
Ibones  and  joints  are  circumscribed  condensations  of  the  mesoderm;  these  condensed 
parts  become  chondrified  and  finally  ossified  to  form  the  bones  of  the  skeleton. 
The  inter\Tning  non-condensed  portions  consist  at  first  of  undifferentiated  meso- 
derm, which  may  develop  in  one  of  three  directions.  It  may  be  converted  into 
fibrous  tissue  as  in  the  case  of  the  skull  bones,  a  synarthrodia!  joint  being  the 
result,  or  it  may  become  partly  cartilaginous,  in  which  case  an  amphiarthrodial 
joint  is  formed.  Again,  it  may  become  looser  in  texture  and  a  cavity  ultimately 
appear  in  its  midst;  the  cells  lining  the  sides  of  this  cavity  form  a  synovial  mem- 
brane and  thus  a  diarthrodial  joint  is  developed. 

The  tissue  surrounding  the  original  mesodermal  core  forms  fibrous  sheaths  for 
the  developing  bones,  i.  e.,  periosteum  and  perichondrium,  which  are  continued 
between  the  ends  of  the  bones  over  the  synovial  membrane  as  the  capsules  of  the 
joints.  These  capsules  are  not  of  uniform  thickness,  so  that  in  them  may  be 
recognized  especially  strengthened  bands  which  are  described  as  ligaments.  This, 
however,  is  not  the  only  method  of  formation  of  ligaments.  In  some  cases  by 
modification  of,  or  derivations  from,  the  tendons  surrounding  the  joint,  additional 
ligamentous  bands  are  provided  to  further  strengthen  the  articulations. 

In  several  of  the  movable  joints  the  mesoderm  which  originally  existed  between 
the  ends  of  the  bones  does  not  become  completely  absorbed — a  portion  of  it 
persists  and  forms  an  articular  disk.  These  disks  may  be  intimately  associated  in 
their  development  with  the  muscles  surrounding  the  joint,  e.  g.,  the  menisci  of  the 
knee-joint,  or  with  cartilaginous  elements,  representatives  of  skeletal  structures, 
which  are  vestigial  in  human  anatomy,  e.  g.,  the  articular  disk  of  the  sterno- 
clavicular joint. 


^ 


284 


SYNDESMOLOGY 


CLASSIFICATION   OF  JOINTS. 

The  articulations  are  divided  into  three  classes:  synarthroses  or  immovablej 
amphiarthroses  or  slightly  movable,  and  diarthroses  or  freely  movable,  joints. 

Synarthroses  {immovable  articulations). — Synarthroses  include  all  those  articu- 
lations in  which  the  surfaces  of  the  bones  are  in  almost  direct  contact,  fastened 
together  by  intervening  connective  tissue  or  hyaline  cartilage,  and  in  which  there 
is  no  appreciable  motion,  as  in  the  joints  between  the  bones  of  the  skull,  excepting 
those  of  the  mandible.  There  are  four  varieties  of  synarthrosis :  sutura,  schindylesis, 
gomphosis,  and  sjmchondrosis. 

Sutura.— Sutura  is  that  form  of  articulation  where  the  contiguous  margins  of  the 
bones  are  united  by  a  thin  layer  of  fibrous  tissue;  it  is  met  with  only  in  the  skull 
(Fig.  296).  When  the  margins  of  the  bones  are  connected  by  a  series  of  processes, 
and  indentations  interlocked  together,  the  articulation  is  termed  a  true  suture 
(sutura  vera) ;  and  of  this  there  are  three  varieties :  sutura  dentata,  serrata,  and 
limbosa.  The  margins  of  the  bones  are  not  in  direct  contact,  being  separated  by  a 
thin  layer  of  fibrous  tissue,  continuous  externally  with  the  pericranium,  internally 
with  the  dura  mater.  The  sutura  dentata  is  so  called  from  the  tooth-like  form  of 
the  projecting  processes,  as  in  the  suture  between  the  parietal  bones.     In  the 


Periosteum 


Sutural  ligament 


Cartilage 


FiQ.  296. — Section  across  the  sagittal  suture. 


Perichondrium 

Periosteum 

Fig.  297. — Section  through  occipitosphenoid  synchon- 
drosis of  an  infant. 


sutura  serrata  the  edges  of  the  bones  are  serrated  like  the  teeth  of  a  fine  saw,  as 
between  the  two  portions  of  the  frontal  bone.  In  the  sutura  limbosa,  there  is  besides 
the  interlocking,  a  certain  degree  of  bevelling  of  the  articular  surfaces,  so  that  the 
bones  overlap  one  another,  as  in  the  suture  between  the  parietal  and  frontal  bones. 
When  the  articulation  is  formed  by  roughened  surfaces  placed  in  apposition  with 
one  another,  it  is  termed  a  false  suture  (sutura  notha),  of  which  there  are  two  kinds: 
the  sutura  squamosa,  formed  by  the  overlapping  of  contiguous  bones  by  broad 
bevelled  margins,  as  in  the  squamosal  suture  between  the  temporal  and  parietal, 
and  the  sutura  harmonia,  where  there  is  simple  apposition  of  contiguous  rough 
surfaces,  as  in  the  articulation  between  the  maxillae,  or  between  the  horizontal 
parts  of  the  palatine  bones. 

Schindylesis. — Schindylesis  is  that  form  of  articulation  in  which  a  thin  plate 
of  bone  is  received  into  a  cleft  or  fissure  formed  by  the  separation  of  two  laminae  in 
another  bone,  as  in  the  articulation  of  the  rostrum  of  the  sphenoid  and  perpendicular 
plate  of  the  ethmoid  with  the  vomer,  or  in  the  reception  of  the  latter  in  the  fissure 
between  the  maxillae  and  between  the  palatine  bones. 

Gomphosis. — Gomphosis  is  articulation  by  the  insertion  of  a  conical  process  into 
a  socket;  this  is  not  illustrated  by  any  articulation  between  bones,  properly  so 
called,  but  is  seen  in  the  articulations  of  the  roots  of  the  teeth  with  the  alveoli 
of  the  mandible  and  maxillae. 

Synchondrosis. — ^Where  the  connecting  medium  is  cartilage  the  joint  is  termed 
a  synchondrosis  (Fig.  297).  This  is  a  temporary  form  of  joint,  for  the  cartilage 
is  converted  into  bone  before  adult  life.  Such  joints  are  found  between  the 
epiphyses  and  bodies  of  long  bones,  between  the  occipital  and  the  sphenoid  at, 
and  for  some  years  after,  birth,  and  between  the  petrous  portion  of  the  temporal 
and  the  jugular  process  of  the  occipital. 


CLASSIFICATION  OF  JOINTS 


285 


Amphiarthroses  {slightly  movable  articulations)  .^In  these  articulations  the 
contiguous  bony  surfaces  are  either  connected  by  broad  flattened  disks  of  fibro- 
cartilage,  of  a  more  or  less  complex  struc- 
ture, as  in  the  articulations  between  the 
bodies  of  the  vertebrae;  or  are  united  by  an 
interosseous  ligament,  as  in  the  inferior 
tibiofibular  articulation.  The  first  form  is 
termed  a  symphysis  (Fig.  298),  the  second 
a  sjmdesmosis. 

Diarthroses  (freely  movable  articulations). 
— This  class  includes  the  greater  number 

of  the  joints  in  the  body.  In  a  diarthrodial  joint  the  contiguous  bony  surfaces 
are  covered  with  articular  cartilage,  and  connected  by  ligaments  lined  by  synovial 
membrane  (Fig.  299).  The  joint  may  be  divided,  completely  or  incompletely, 
by  an  articular  disk  or  meniscus,  the  periphery  of  which  is  continuous  with 
the  fibrous  capside  while  its  free  surfaces  are  covered  by  synovial  membrane 
(Fig.  300). 


Ligament 

Disc  of 
fibrocartilage 
Articular  cartilage. 


Fig.  298. — Diagrammatic  section  of  a  symphysis. 


Articular  cartilage 

Synovial  1 

stratum  \  Articular 
Fibrous  I  capsule 
stratum  J 


Synovial  stratum 
Articular  cartilage 
Articular  disk 


Fibrous  stratum 


Fig.  299. — Diagrammatic  section  of  a  diarthrodial  joint. 


Fig.  300. — Diagrammatic  section  of  a  diarthrodial 
joint,  with  an  articular  disk. 


P 
I 

II 


The  varieties  of  joints  in  this  class  have  been  determined  by  the  kind  of  motion 
permitted  in  each.  There  are  two  varieties  in  which  the  movement  is  uniaxial,  that 
is  to  say,  all  movements  take  place  around  one  axis.  In  one  form,  the  gingl3rmus, 
,  this  axis  is,  practically  speaking,  transverse;  in  the  other,  the  trochoid  or  pivot- 
fejoint,  it  is  longitudinal.  There  are  two  varieties  where  the  movement  is  biaxial, 
or  around  two  horizontal  axes  at  right  angles  to  each  other,  or  at  any  intervening 
axis  between  the  two.    These  are  the  condyloid  and  the  saddle-joint.      There  is 

(one  form  where  the  movement  is  polyaxial,  the  enarthrosis  or  ball-and-socket  joint; 
and  finally  there  are  the  arthrodia  or  gliding  joints. 
Ginglymus  or  Hinge-joint.- — In  this  form  the  articular  surfaces  are  moulded 
to  each  other  in  such  a  manner  as  to  permit  motion  only  in  one  plane,  forward 
and  backward,  the  extent  of  motion  at  the  same  time  being  considerable.  The 
direction  which  the  distal  bone  takes  in  this  motion  is  seldom  in  the  same  plane 
as  that  of  the  axis  of  the  proximal  bone;  there  is  usually  a  certain  amount  of  devia- 
tion from  the  straight  line  during  flexion.  The  articular  surfaces  are  connected 
together  by  strong  collateral  ligaments,  which  form  their  chief  bond  of  union. 
The  best  examples  of  ginglymus  are  the  interphalangeal  joints  and  the  joint  between 
the  humerus  and  ulna;  the  knee-  and  ankle-joints  are  less  typical,  as  they  allow 
a  slight  degree  of  rotation  or  of  side-to-side  movement  in  certain  positions  of  the 
limb. 

Trochoid  or  Pivot-joint  (articulatio  trochoidea;  rotary  joint) . — Where  the  movement 
is  limited  to  rotation,  the  joint  is  formed  by  a  pivot-like  process  turning  within 


L. 


286  ^m^^V  SYNDESMOLOGY 

a  ring,  or  a  ring  on  a  pivot,  the  ring  being  formed  partly  of  bone,  partly  of  ligament. 
In  the  proximal  radioulnar  articulation,  the  ring  is  formed  by  the  radial  notch 
of  the  ulna  and  the  annular  ligament;  here,  the  head  of  the  radius  rotates  within 
the  ring.  In  the  articulation  of  the  odontoid  process  of  the  axis  with  the  atlas 
the  ring  is  formed  in  front  by  the  anterior  arch,  and  behind  by  the  transverse 
ligament  of  the  atlas;  here,  the  ring  rotates  around  the  odontoid  process. 

Condyloid  Articulation  (articidatio  ellipsoidea) .■ — In  this  form  of  joint,  an  ovoid 
articular  surface,  or  condyle,  is  received  into  an  elliptical  cavity  in  such  a  manner 
as  to  permit  of  flexion,  extension,  adduction,  abduction,  and  circumduction,  but 
no  axial  rotation.    The  wrist-joint  is  an  example  of  this  form  of  articulation. 

Articulation  by  Reciprocal  Reception  {articulatio  sellaris;  saddle-joint). — In  this 
variety  the  opposing  surfaces  are  reciprocally  concavo-convex.  The  movements 
are  the  same  as  in  the  preceding  form;  that  is  to  say,  flexion,  extension,  adduction, 
abduction,  and  circumduction  are  allowed ;  but  no  axial  rotation.  The  best  example 
of  this  form  is  the  carpometacarpal  joint  of  the  thumb. 

Enarthrosis  {ball-and-socket  joints) . — Enarthrosis  is  a  joint  in  which  the  distal 
bone  is  capable  of  motion  around  an  indefinite  number  of  axes,  which  have  one 
common  center.  It  is  formed  by  the  reception  of  a  globular  head  into  a  cup-like 
cavity,  hence  the  name  "ball-and-socket."  Examples  of  this  form  of  articulation 
are  found  in  the  hip  and  shoulder. 

Arthrodia  (gliding  joints)  is  a  joint  which  admits  of  only  gliding  movement;  it 
is  formed  by  the  apposition  of  plane  surfaces,  or  one  slightly  concave,  the  other 
slightly  convex,  the  amount  of  motion  between  them  being  limited  by  the  ligaments 
or  osseous  processes  surrounding  the  articulation.  It  is  the  form  present  in  the 
joints  between  the  articular  processes  of  the  vertebrae,  the  carpal  joints,  except 
that  of  the  capitate  with  the  navicular  and  lunate,  and  the  tarsal  joints  with  the 
exception  of  that  between  the  talus  and  the  navicular. 


THE  KINDS  OF  MOVEMENT  ADMITTED  IN  JOINTS. 

The  movements  admissible  in  joints  may  be  divided  into  four  kinds:  gliding 
and  angular  movements,  circumduction,  and  rotation.  These  movements  are  often, 
however,  more  or  less  combined  in  the  various  joints,  so  as  to  produce  an  infinite 
variety,  and  it  is  seldom  that  only  one  kind  of  motion  is  found  in  any  particular 
joint. 

Gliding  Movement. — Gliding  movement  is  the  simplest  kind  of  motion  that  can 
take  place  in  a  joint,  one  surface  gliding  or  moving  over  another  without  any 
angular  or  rotatory  movement.  It  is  common  to  all  movable  joints ;  but  in  some, 
as  in  most  of  the  articulations  of  the  carpus  and  tarsus,  it  is  the  only  motion  per- 
mitted. This  movement  is  not  confined  to  plane  surfaces,  but  may  exist  between 
any  two  contiguous  surfaces,  of  whatever  form. 

Angular  Movement.^ — Angular  movement  occurs  only  between  the  long  bones, 
and  by  it  the  angle  between  the  two  bones  is  increased  or  diminished.  It  may 
take  place:  (1)  forward  and  backward,  constituting  flexion  and  extension;  or  (2) 
toward  and  from  the  median  plane  of  the  body,  or,  in  the  case  of  the  fingers  or 
toes,  from  the  middle  line  of  the  hand  or  foot,  constituting  adduction  and  abduction. 
The  strictly  ginglymoid  or  hinge-joints  admit  of  flexion  and  extension  only.  Abduc- 
tion and  adduction,  combined  with  flexion  and  extension,  are  met  with  in  the  more 
movable  joints;  as  in  the  hip,  the  shoulder,  the  wrist,  and  the  carpometacarpal 
joint  of  the  thumb. 

Circumduction.^ — Circumduction  is  that  form  of  motion  which  takes  place  between 
the  head  of  a  bone  and  its  articular  cavity,  when  the  bone  is  made  to  circumscribe 
a  conical  space;  the  base  of  the  cone  is  described  by  the  distal  end  of  the  bone, 


ARTICULATIONS  OF  THE  VERTEBRAL  COLUMN 


287 


II 


the  apex  is  in  the  articular  cavity;  this  kind  of  motion  is  best  seen  in  the  shoulder- 
and  hip-joints. 

Rotation. — Rotation  is  a  form  of  movement  in  which  a  bone  moves  around  a 
central  axis  without  undergoing  any  displacement  from  this  axis;  the  axis  of  rota- 
tion may  lie  in  a  separate  bone,  as  in  the  case  of  the 'pivot  formed  by  the  odontoid 
process  of  the  axis  vertebrae  around  which  the  atlas  turns;  or  a  bone  may  rotate 
around  its  own  longitudinal  axis,  as  in  the  rotation  of  the  humerus  at  the  shoulder- 
joint;  or  the  axis  of  rotation  may  not  be  quite  parallel  to  the  long  axis  of  the 
bone,  as  in  the  movement  of  the  radius  on  the  ulna  during  pronation  and  supina- 
tion of  the  hand,  where  it  is  represented  by  a  line  connecting  the  center  of  the 
head  of  the  radius  above  with  the  center  of  the  head  of  the  ulna  below. 

Ligamentous  Action  of  Muscles. — The  movements  of  the  different  joints  of  a  limb  are  combined 
by  means  of  the  long  muscles  passing  over  more  than  one  joint.  These,  when  relaxed  and  stretched 
to  their  greatest  extent,  act  as  elastic  ligaments  in  restraining  certain  movements  of  one  joint, 
except  when  combined  with  corresponding  movements  of  the  other — the  latter  movements  being 
usually  in  the  opposite  direction.  Thus  the  shortness  of  the  hamstring  muscles  prevents  com- 
plete flexion  of  the  hip,  unless  the  knee-joint  is  also  flexed  so  as  to  bring  their  attachments  nearer 
together.  The  uses  of  this  arrangement  are  threefold:  (1)  It  coordinates  the  kinds  of  move- 
ments which  are  the  most  habitual  and  necessary,  and  enables  them  to  be  performed  with  the 
least  expenditmre  of  power.  (2)  It  enables  the  short  muscles  which  pass  over  only  one  joint  to 
act  upon  more  than  one.  (3)  It  provides  the  joints  with  ligaments  which,  while  they  are  of  very 
great  power  in  resisting  movements  to  an  extent  incompatible  with  the  mechanism  of  the  joint, 
at  the  same  time  spontaneously^  yield  when  necessary. 

The  articulations  may  be  grouped  into  those  of  the  trunk,  and  those  of  the  upper 
and  lower  extremities. 


ARTICULATIONS   OF   THE   TRUNK. 

These  may  be  divided  into  the  following  groups,  viz.: 


I.  Of  the  Vertebral  Column.  VI. 

II.  Of  the  Atlas  with  the  Axis. 
III.  Of  the  Vertebral  Column  with      VII. 
the  Cranium.  VIII. 

Of  the  Mandible. 
Of  the  Ribs  with  the  Vertebrae. 


iIV. 
V. 


IX. 


Of  the  Cartilages  of  the  Ribs  with  the 
Sternum,  and  with  Each  Other. 

Of  the  Sternum. 

Of  the  Vertebral  Column  with  the 
Pelvis. 

Of  the  Pelvis. 


I.    Articulations  of  the  Vertebral  Column. 


arthrodial  joints  between  the  vertebral  bodies,  and  (2) 
joints  between  the  vertebral  arches. 

1.  Articulations  of  Vertebral  Bodies  {intercentral  ligaments). — The  articulations 
between  the  bodies  of  the  vertebrae  are  amphiarthrodial  joints,  and  the  individual 
vertebrae  move  only  slightly  on  each  other.  When,  however,  this  slight  degree 
of  movement  between  the  pairs  of  bones  takes  place  in  all  the  joints  of  the  vertebral 
column,  the  total  range  of  movement  is  very  considerable.  The  ligaments  of  these 
articulations  are  the  following: 


a  series  of  amphi- 
a  series  of  diathrodial 


ir 


The  Anterior  Longitudinal.  The  Posterior  Longitudinal. 

The  Intervertebral  Fibrocartilages. 


The  Anterior  Longitudinal  Ligament  {ligavientum  longitudinale  anterius;  anterior 
common  ligament)  (Figs.  301,  312). — The  anterior  longitudinal  ligament  is  a  broad 
and  strong  band  of  fibers,  which  extends  along  the  anterior  surfaces  of  the  bodies 
of  the  vertebrae,  from  the  axis  to  the  sacrum.    It  is  broader  below  than  above, 


288 


SYNDESMOLOGY 


thicker  in  the  thoracic  than  in  the  cervical  and  lumbar  regions,  and  somewhaT 
thicker  opposite  the  bodies  of  the  vertebrae  than  opposite  the  intervertebral  fibro- 
cartilages.  It  is  attached,  above,  to  the  body  of  the  axis,  where  it  is  continuous 
with  the  anterior  atlantoaxial  ligament,  and  extends  down  as  far  as  the  upper 
part  of  the  front  of  the  sacrum.  It  consists  of  dense  longitudinal  fibers,  which 
are  intimately  adherent  to  the  intervertebral  fibrocartilages  and  the  prominent: 
margins  of  the  vertebrae,  but  not  to  the  middle  parts  of  the  bodies.  In  the  latter 
situation  the  ligament  is  thick  and  serves  to  fill  up  the  concavities  on  the  anterior 
surfaces,  and  to  make  the  front  of  the  vertebral  column  more  even.  It  is  composed 
of  several  layers  of  fibers,  which  vary  in  length,  but  are  closely  interlaced  with 
each  other.  The  most  superficial  fibers  are  the  longest  and  extend  between  four 
or  five  vertebrae.  A  second,  subjacent  set  extends  between  two  or  three  vertebrae; 
while  a  third  set,  the  shortest  and  deepest,  reaches  from  one  vertebra  to  the  next. 
At  the  sides  of  the  bodies  the  ligament  consists  of' a  few  short  fibers  which  pass 
from  one  vertebra  to  the  next,  separated  from  the  concavities  of  the  vertebral 
bodies  by  oval  apertures  for  the  passage  of  vessels. 


Fig.  301. — ^Median  sagittal  section  of  two  lumbar  vertebrse  and  their  ligaments. 


The  Posterior  Longitudinal  Ligament  {ligamentum  longitudinale  posteritis;  posterior 
common  ligament)  (Figs.  301,  302).— The  posterior  longitudinal  ligament  is  situated 
within  the.  vertebral  canal,  and  extends  along  the  posterior  surfaces  of  the  bodies 
of  the  vertebrae,  from  the  body  of  the  axis,  where  it  is  continuous  with  the  membrana 
tectoria,  to  the  sacrum.  It  is  broader  above  than  below,  and  thicker  in  the  thoracic 
than  in  the  cervical  and  lumbar  regions.  In  the  situation  of  the  intervertebral 
fibrocartilages  and  contiguous  margins  of  the  vertebrae,  where  the  ligament  is  more 
intimately  adherent,  it  is  broad,  and  in  the  thoracic  and  lumbar  regions  presents 
a  series  of  dentations  with  intervening  concave  margins ;  but  it  is  narrow  and  thick 
over  the  centers  of  the  bodies,  from  which  it  is  separated  by  the  basivertebral 
veins.  This  ligament  is  composed  of  smooth,  shining,  longitudinal  fibers,  denser 
and  more  compact  than  those  of  the  anterior  ligament,  and  consists  of  superficial 
layers  occupying  the  interval  between  three  or  four  vertebrae,  and  deeper  layers 
which  extend  between  adjacent  vertebrae. 


I 


ARTICULATIONS  OF  THE  VERTEBRAL  COLUMN 


289 


I 

H[  The  Intervertebral  Fibrocartilages  (fibrocartilagines  mtervertehrales ;  intervertebral 
^\dis1cs)  (Figs.  301,  313). — The  intervertebral  fibrocartilages  are  interposed  between 
^  the  adjacent  surfaces  of  the  bodies  of  the  vertebrae,  from  the  axis  to  the  sacrum, 

and  form  the  chief  bonds  of  connection  between  the  vertebrae.  They  vary  in  shape, 

size,  and  thickness,  in  different  parts  of  the  vertebral  column.    In  shape  and  size 

they  correspond  with  the  surfaces  of  the  bodies  between  which  they  are  placed. 
Hi  except  in  the  cervical  region,  where  they  are  slightly  smaller  from  side  to  side  than 
™-  the  corresponding  bodies.     In  thickness  they  vary  not  only  in  the  different -regions 

of  the  column,  but  in  different  parts  of  the  same  fibrocartilage;  they  are  thicker 

in  front  than  behind  in  the  cervical  and  lumbar 

regions,  and  thus  contribute  to  the  anterior  con- 
vexities of  these  parts  of  the  column;  while  they 

are  of  nearly  uniform  thickness  in  the  thoracic 

region,  the  anterior  concavity  of  this  part  of 

the  column  being  almost  entirely  owing  to  the 

shape  of  the  vertebral  bodies.  The  interverte- 
bral fibrocartilages  constitute  about  one-fourth 

of  the  length  of  the  vertebral  column,  exclusive 

of  the  first  two  vertebrae;  but  this  amount  is 

not  equally  distributed  between  the  various 

bones,  the  cervical  and  lumbar  portions  having, 

in  proportion  to  their  length,  a  much  greater 

amount  than  the  thoracic  region,  with  the  result 

that  these  parts  possess  greater  pliancy  and 

freedom    of    movement.     The    intervertebral 

H  fibrocartilages  are  adherent,  by  their  surfaces, 
to  thin  layers  of  hyaline  cartilage  which  cover 
the  upper  and  under  surfaces  of  the  bodies  of 
the  vertebrae;  in  the  lower  cervical  vertebrae, 
however,  small  joints  lined  by  synovial  membrane  are  occasionally  present  between 
the  upper  surfaces  of  the  bodies  and  the  margins  of  the  fibrocartilages  on  either 
side.  By  their  circumferences  the  intervertebral  fibrocartilages  are  closely  con- 
nected in  front  to  the  anterior,  and  behind  to  the  posterior,  longitudinal  liga- 
ments. In  the  thoracic  region  they  are  joined  laterally,  by  means  of  the  inter- 
articular  ligaments,  to  the  heads  of  those  ribs  which  articulate  with  two  vertebrae. 


Pedicle  {cut) 


Intervertebral 
fibrocartilage 


Fig.  302.- 


-Poaterior  longitudinal  ligament,  in 
the  thoracic  region. 


II 


Structure  of  the  Intervertebral  Fibrocartilages. — Each  is  composed,  at  its  circumference,  of 
laminse  of  fibrous  tissue  and  fibrocartilage,  forming  the  annulus  fibrosus;  and,  at  its  center,  of 
a  soft,  pulpy,  highly  elastic  substance,  of  a  yellowish  color,  which  projects  considerably  above 
the  surrounding  level  when  the  disk  is  divided  horizontally.  This  pulpy  substance  {nucleus 
pulposus),  especially  well-developed  in  the  lumbar  region,  is  the  remains  of  the  notochord.  The 
laminae  are  arranged  concentrically;  the  outermost  consist  of  ordinary  fibrous  tissue,  the  others 
of  white  fibrocartilage.  The  laminae  are  not  quite  vertical  in  their  direction,  those  near  the  cir- 
cumference being  curved  outward  and  closely  approximated;  while  those  nearest  the  center 
curve  in  the  opposite  direction,  and  are  somewhat  more  widely  separated.  The  fibers  of  which 
each  lamina  is  composed  are  directed,  for  the  most  part,  obhquely  from  above  downward,  the 
fibers  of  adjacent  laminae  passing  in  opposite  directions  and  varying  in  every  layer;  so  that  the 
fibers  of  one  layer  are  directed  across  those  of  another,  like  the  limbs  of  the  letter  X.  This  laminar 
arrangement  belongs  to  about  the  outer  half  of  each  fibrocartilage.  The  pulpy  substance  presents 
no  such  arrangement,  and  consists  of  a  fine  fibrous  matrix,  containing  angular  cells  united  to 
form  a  reticular  structure. 

The  intervertebral  fibrocartilages  are  important  shock  absorbers.  Under  pressure  the  highly 
elastic  nucleus  pulposus  becomes  flatter  and  broader  and  pushes  the  more  resistant  fibrous  laminae 
outward  in  all  directions. 

2.  Articulations  of  Vertebral  Arches. — The  joints  between  the  articular  pro- 
cesses of  the  vertebrae  belong  to  the  arthrodial  variety  and  are  enveloped  by 

19 


II 


SYNDESMOLOGY 


I 


capsules  lined  by  synovial  membranes;  while  the  laminse,  spinous  and  transvers(? 
processes  are  connected  by  the  following  ligaments: 


The  Ligamentum  Nuchse. 
The  Interspinal. 
The  Intertransverse. 


The  Ligamenta  Flava. 
The  Supraspinal. 

il 

The  Articular  Capsules  (capsules  articulares;  capsular  ligaments)  (Fig.  301). — 
The  articular  capsules  are  thin  and  loose,  and  are  attached  to  the  margins  of  the 
articular  processes  of  adjacent  vertebrae.  They  are  longer  and  looser  in  the  cervical 
than  in  the  thoracic  and  lumbar  regions. 

The  Ligamenta  Flava  (ligamenta  subfiava,  Fig.  303). — The  ligamenta  flava  connect 
the  laminae  of  adjacent  vertebrae,  from  the  axis  to  the  first  segment  of  the  sacrum. 
They  are  best  seen  from  the  interior  of  the  vertebral  canal ;  when  looked  at  from  the 
outer  surface  they  appear  short,  being  overlapped  by  the  laminae.  Each  ligament 
consists  of  two  lateral  portions  w^hich  commence  one  on  either  side  of  the  roots 
of  the  articular  processes,  and  extend  backw^ard  to  the  point  where  the  laminae 
meet  to  form  the  spinous  process ;  the  posterior  margins  of  the  tw^o  portions  are  in 
contact  and  to  a  certain  extent  united,  slight  intervals  being  left  for  the  passage 
of  small  vessels.   Each  consists  of  yellow  elastic  tissue,  the  fibers  of  which,  almost 

perpendicular  in  direction,  are  at- 
tached to  the  anterior  surface  of 
the  lamina  above,  some  distance 
from  its  inferior  margin,  and  to  the 
posterior  surface  and  upper  margin 
of  the  lamina  below.  In  the  cervical 
region  the  ligaments  are  thin,  but 
broad  and  long;  they  are  thicker  in 
the  thoracic  region,  and  thickest  in 
the  lumbar  region.  Their  marked 
elasticity  serves  to  preserve  the  up- 
right posture,  and  to  assist  the 
vertebral  column  in  resuming  it 
after  flexion. 

The  Supraspinal  Ligament  (liga- 
mentum supraspinale;  supraspinous 
ligament)  (Fig.  301). — The  supra- 
spinal ligament  is  a  strong  fibrous 
cord,  which  connects  together  the 
apices  of  the  spinous  processes  from 
the  seventh  cervical  vertebra  to  the  sacrum ;  at  the  points  of  attachment  to  the 
tips  of  the  spinous  processes  fibrocartilage  is  developed  in  the  ligament.  It  is 
thicker  and  broader  in  the  lumbar  than  in  the  thoracic  region,  and  intimately 
blended,  in  both  situations,  with  the  neighboring  fascia.  The  most  superficial 
fibers  of  this  ligament  extend  over  three  or  four  vertebrae;  those  more  deeply 
seated  pass  between  two  or  three  vertebrae;  while  the  deepest  connect  the  spinous 
processes  of  neighboring  vertebrae.  Between  the  spinous  processes  it  is  continuous 
with  the  interspinal  ligaments.  It  is  continued  upward  to  the  external  occipital 
protuberance  and  median  nuchal  line,  as  the  ligamentum  nuchae. 

The  Ligamentum  Nuchas. — The  ligamentum  nuchae  is  a  fibrous  membrane,  which, 
in  the  neck,  represents  the  supraspinal  ligaments  of  the  lower  vertebrae.  It  extends 
from  the  external  occipital  protuberance  and  median  nuchal  line  to  the  spinous 
process  of  the  seventh  cervical  vertebra.  From  its  anterior  border  a  fibrous  lamina 
is  given  off,  which  is  attached  to  the  posterior  tubercle  of  the  atlas,  and  to  the 
spinous  processes  of  the  cervical  vertebrae,  and  forms  a  septum  between  the  muscles 


Pedicle  {cut) 


Lamina 


Fig.  303. — Vertebral  arches  of  three  thoracic  vertebrae 
viewed  from  the  front. 


ARTICULATIONS  OF  THE  VERTEBRAL  COLUMN  291 

on  either  side  of  the  neck.  In  man  it  is  merely  the  rudiment  of  an  important  elastic 
ligament,  which,  in  some  of  the  lower  animals,  serves  to  sustain  the  weight  of  the 
head. 

The  Interspinal  Ligaments  (ligamenta  inter spinalia;  interspinous  ligaments) 
(Fig.  301). — The  interspinal  ligaments  thin  and  membranous,  connect  adjoining 
spinous  processes  and  extend  from  the  root  to  the  apex  of  each  process.  They 
meet  the  ligamenta  flava  in  front  and  the  supraspinal  ligament  behind.  They 
are  narrow  and  elongated  in  the  thoracic  region;  broader,  thicker,  and  quadrilateral 
in  form  in  the  lumbar  region;  and  only  slightly  developed  in  the  neck. 

The  Intertransverse  Ligaments  (ligamenta  intertransversaria) . — The  intertransverse 
ligaments  are  interposed  between  the  transverse  processes.  In  the  cervical  region 
they  consist  of  a  few  irregular,  scattered  fibers;  in  the  thoracic  region  they  are 
rounded  cords  intimately  connected  with  the  deep  muscles  of  the  back;  in  the 
lumbar  region  they  are  thin  and  membranous. 

Movements. — The  movements  permitted  in  the  vertebral  column  are:  flexion,  extension, 
lateral  movement,  circumduction,  and  rotation. 

In  flexion,  or  movement  forward,  the  anterior  longitudinal  ligament  is  relaxed,  and  the  inter- 
vertebral fibrocartilages  are  compressed  in  front;  while  the  posterior  longitudinal  ligament,  the 
ligamenta  flava,  and  the  inter-  and  supraspinal  ligaments  are  stretched,  as  well  as  the  posterior 
fibers  of  the  intervertebral  fibrocartUages.  The  interspaces  between  the  laminae  are  widened, 
and  the  inferior  articular  processes  gUde  upward,  upon  the  superior  articular  processes  of  the 
subjacent  vertebrae.  Flexion  is  the  most  extensive  of  aU  the  movements  of  the  vertebral  column, 
and  is  freest  in  the  lumbar  region. 

In  extension,  or  movement  backward,  an  exactly  opposite  disposition  of  the  parts  takes  place. 
This  movement  is  limited  by  the  anterior  longitudinal  hgament,  and  by  the  approximation  of 
the  spinous  processes.    It  is  freest  in  the  cervical  region. 

In  lateral  movement,  the  sides  of  the  intervertebral  fibrocartilages  are  compressed,  the  extent 
of  motion  being  limited  by  the  resistance  offered  by  the  surrounding  hgaments.  This  movement 
may  take  place  in  any  part  of  the  column,  but  is  freest  in  the  cervical  and  lumbar  regions. 

Circumduction  is  very  Umited,  and  is  merely  a  succession  of  the  preceding  movements. 

Rotation  is  produced  by  the  twisting  of  the  intervertebral  fibrocartilages;  this,  although  only 
slight  between  any  two  vertebrae,  allows  of  a  considerable  extent  of  movement  when  it  takes  place 
in  the  whole  length  of  the  column,  the  front  of  the  upper  part  of  the  column  being  turned  to  one 
or  other  side.  This  movement  occurs  to  a  sUght  extent  in  the  cervical  region,  is  freer  in  the  upper 
part  of  the  thoracic  region,  and  absent  in  the  lumbar  region. 

The  extent  and  variety  of  the  movements  are  influenced  by  the  shape  and  direction  of  the 
articular  surfaces.  In  the  cervical  region  the  upward  incUnation  of  the  superior  articular  surfaces 
allows  of  free  flexion  and  extension.  Extension  can  be  carried  farther  than  flexion;  at  the  upper 
end  of  the  region  it  is  checked  by  the  locking  of  the  posterior  edges  of  the  superior  atlantal  facets 
in  the  condyloid  fossae  of  the  occipital  bone;  at  the  lower  end  it  is  limited  by  a  mechanism  whereby 
the  inferior  articular  processes  of  the  seventh  cervical  vertebra  slip  into  grooves  behind  and 
below  the  superior  articular  processes  of  the  first  thoracic.  Flexion  is  arrested  just  beyond  the 
point  where  the  cervical  convexity  is  straightened;  the  movement  is  checked  by  the  apposition 
of  the  projecting  lower  hps  of  the  bodies  of  the  vertebrae  with  the  shelving  surfaces  on  the  bodies 
of  the  subjacent  vertebrae.  Lateral  flexion  and  rotation  are  free  in  the  cervical  region;  they  are, 
however,  always  combined.  The  upward  and  medial  inclinations  of  the  superior  articular  surfaces 
impart  a  rotatory  movement  during  lateral  flexion,  while  pure  rotation  is  prevented  by  the  slight 
medial  slope  of  these  surfaces. 

In  the  thoracic  region,  notably  in  its  upper  part,  all  the  movements  are  limited  in  order  to 
reduce  interference  with  respiration  to  a  minimum.  The  almost  complete  absence  of  an  upward 
inclination  of  the  superior  articular  surfaces  prohibits  any  marked  flexion,  while  extension  is 
checked  by  the  contact  of  the  inferior  articular  margins  with  the  laminae,  and  the  contact  of  the 
spinous  processes  with  one  another.  The  mechanism  between  the  seventh  cervical  and  the  first 
thoracic  vertebrae,  which  Umits  extension  of  the  cervical  region,  will  also  ser\'e  to  limit  flexion  of 
the  thoracic  region  when  the  neck  is  extended.  Rotation  is  free  in  the  thoracic  region:  the 
superior  articular  processes  are  segments  of  a  cyUnder  whose  axis  is  in  the  mid-ventral  line  of  the 
vertebral  bodies.  The  direction  of  the  articular  facets  would  allow  of  free  lateral  flexion,  but 
this  movement  is  considerably  limited  in  the  upper  part  of  the  region  by  the  resistance  of  the 
ribs  and  sternum. 

In  the  lumbar  region  flexion  and  extension  are  free.  Flexion  can  be  carried  farther  than  exten- 
sion, and  is  possible  to  just  beyond  the  straightening  of  the  lumbar  curve;  it  is,  therefore,  greatest 
at  the  lowest  part  where  the  curve  is  sharpest.    The  inferior  articular  facets  are  not  in  close  appo- 


292 


SYNDESMOLOGY 


sition  with  the  superior  facets  of  the  subjacent  vertebrae,  and  on  this  account  a  considerable 
amount  of  lateral  flexion  is  permitted.  For  the  same  reason  a  slight  amount  of  rotation  can  be 
carried  out,  but  this  is  so  soon  checked  by  the  interlocking  of  the  articular  surfaces  that  it  is 
negligible. 

The  principal  muscles  which  produce  flexion  are  the  Sternocleidomastoideus,  Longus  capitis, 
and  Longus  colh;  the  Scaleni;  the  abdominal  muscles  and  the  Psoas  major.  Extension  is  produced 
by  the  intrinsic  muscles  of  the  back,  assisted  in  the  neck  by  the  Splenius,  Semispinales  dorsi  and 
cervicis,  and  the  Multifidus.  Lateral  motion  is  produced  by  the  intrinsic  muscles  of  the  back 
by  the  Splenius,  the  Scaleni,  the  Quadratus  lumborum,  and  the  Psoas  major,  the  muscles  of  one 
side  only  acting;  and  rotation  by  the  action  of  the  following  muscles  of  one  side  only,  viz.,  the 
Sternocleidomastoideus,  the  Longus  capitis,  the  Scaleni,  the  Multifidus,  the  SemispinaUs  capitis, 
and  the  abdominal  muscles. 


n.    Articulation  of  the  Atlas  with  the  Epistropheus  or  Axis  (Articulatio 

Atlantoepistrophica) . 


*l 


The  articulation  of  the  atlas  with  the  axis  is  of  a  complicated  nature,  com- 
prising no  fewer  than  four  distinct  joints.  There  is  a  pivot  articulation  between 
the  odontoid  process  of  the  axis  and  the  ring  formed  by  the  anterior  arch  and 
the  tranverse  ligament  of  the  atlas  (see  Fig.  306);  here  there  are  two  joints:  one 
between  the  posterior  surface  of  the  anterior  arch  of  the  atlas  and  the  front  of 
the  odontoid  process;  the  other  between  the  anterior  surface  of  the  ligament  and 
the  back  of  the  process.  Between  the  articular  processes  of  the  two  bones  there 
is  on  either  side  an  arthrodial  or  gliding  joint.  The  ligaments  connecting  these 
bones  are: 


Two  Articular  Capsules. 
The  Anterior  Atlantoaxial. 


The  Posterior  Atlantoaxial. 
The  Transverse. 


Atlanto- 

occipital      f  Articular  capsule 

— ■ '.  and 

[^synovial  membrane 


C  Articular  capgule 
<  and 

ysynovial  membrane 


Fig.  304. — Anterior  atlantooccipital  membrane  and  atlantoaxial  ligament. 


q 


The  Articular  Capsules  (capsulce  articulares;  capsular  ligaments). — The  articular 
capsules  are  thin  and  loose,  and  connect  the  margins  of  the  lateral  masses  of  the 
atlas  with  those  of  the  posterior  articular  surfaces  of  the  axis.  Each  is  strength- 
ened at  its  posterior  and  medial  part  by  an  accessory  ligament,  which  is  attached 


[RTICULATION  OF  THE  ATLAS  WITH  THE  EPISTROPHEUS  OR  AXIS 


)elow  to  the  body  of  the  axis  near  the  base  of  the  odontoid  process,  and  above 
to  the  lateral  mass  of  the  atlas  near  the  transverse  ligament. 

The  Anterior  Atlantoaxial  Ligament  (Fig.  304). — This  ligament  is  a  strong  mem- 
brane, fixed,  above,  to  the  lower  border  of  the  anterior  arch  of  the  atlas;  below, 
to  the  front  of  the  body  of  the  axis.    It  is  strengthened  in  the  middle  line  by  a 


Arch  for  passage  of 
vertebral  artery 
and  first  cervical 
nerve 


Fig.  305. — Posterior  atlantooccipital  membrane  and  atlantoaxial  ligament. 

rounded  cord,  which  connects  the  tubercle  on  the  anterior  arch  of  the  atlas  to  the 
body  of  the  axis,  and  is  a  continuation  upward  of  the  anterior  longitudinal  liga- 
ment.   The  ligament  is  in  relation,  in  front,  with  the  Longi  capitis. 


Fig.  306. — Articulation  between  odontoid  process  and  atlas. 

The  Posterior  Atlantoaxial  Ligament  (Fig.  305). — This  ligament  is  a  broad,  thin 
"membrane  attached,  above,  to  the  lower  border  of  the  posterior  arch  of  the  atlas; 
beloui,  to  the  upper  edges  of  the  laminae  of  the  axis.  It  supplies  the  place  of 
the  ligamenta  flava,  and  is  in  relation,  behind,  with  the  Obliqui  capitis  inferiores. 

The  Transverse  Ligament  of  the  Atlas  (ligamentum  transversum  atlantis)  (Figs. 
306,  307,  308) . — The  transverse  ligament  of  the  atlas  is  a  thick,  strong  band,  which 


294 


SYNDESMOLOGY 


Apical  odontoid 
ligament 


Atlanta.  (  Articular  capsule 
and 


■{.. 


^ifr\    '^'^P'^^'^^synovial  membrane 


.^■,     .     f  Artyyular  caps^de 
Atlanta-)  ^„^j  ^ 

axial    y  synovial  membrane 


Fia.  307. — Membrana  tectoria,  transverae,  and  alar  ligament3. 


Superficial  layer  of  menibrana  tectoria 


Anterior  atlanto- 
occipital  membrane 

Membrana  tectoria 

Cms  swperius  of 

transverse  ligament 

Apical  odont.  lig. 

Ant.  arch  of  atlas 

Odontoid  process, 
of  axis 
Articular  cavity 

Transverse  ligament 

Anterior  atlanto- 
axial ligament 


Jntervertebral 
Jibrocartilage 


Anterior  longitudinal 
ligament 


Posterior  atlanto- 
ipiial  membrane 

Posterior  arch 
of  atlas 

itboccipital  nerve 


Posterior  longitudinal  ligament 
Fia.  308  —Median  sagittal  section  through  the  occipital  bone  and  first  three  cervical  vertebra.      (Spaltehola.) 


I  ARTICULATIONS  OF  THE  VERTEBRAL  COLUMN  WITH  THE  CRANIUM  295 
arches  across  the  ring  of  the  atlas,  and  retains  the  odontoid  process  in  contact  with 
the  anterior  arch.  It  is  concave  in  front,  convex  behind,  broader  and  thicker  in 
the  middle  than  at  the  ends,  and  firmly  attached  on  either  side  to  a  small  tubercle 
on  the  medial  surface  of  the  lateral  mass  of  the  atlas.  As  it  crosses  the  odontoid 
process,  a  small  fasciculus  (crus  superius)  is  prolonged  upward,  and  another  (cms 

II  inferius)  downward,  from  the  superficial  or  posterior  fibers  of  the  ligament.    The 
I  former  is  attached  to  the  basilar  part  of  the  occipital  bone,  in  close  relation  with 
I  the  membrana  tectoria;  the  latter  is  fixed  to  the  posterior  surface  of  the  body 
jof  the  axis;  hence,  the  whole  ligament  is  named  the  cruciate  ligament  of  the  atlas. 
I  The  transverse  ligament  divides  the  ring  of  the  atlas  into  two  unequal  parts: 
j  of  these,  the  posterior  and  larger  serves  for  the  transmission  of  the  medulla  spinalis 
land  its  membranes  and  the  accessory  nerves;  the  anterior  and  smaller  contains 
\  the  odontoid  process.    The  neck  of  the  odontoid  process  is  constricted  where  it  is 
embraced  posteriorly  by  the  transverse  ligament,  so  that  this  ligament  suffices 
^   to  retain  the  odontoid  process  in  position  after  all  the  other  ligaments  have  been 
Hi  divided. 

^■1  S3movial  Membranes. — There  is  a  synovial  membrane  for  each  of  the  four  joints;  the  joint 
^■f  cavity  between  the  odontoid  process  and  the  transverse  hgament  is  often  continuous  with  those 
of  the  atlantooccipital  articulations. 

Movements. — The  opposed  articular  surfaces  of  the  atlas  and  axis  are  not  reciprocally  curved; 
both  surfaces  are  convex  in  their  long  axes.  When,  therefore,  the  upper  facet  glides  forward 
on  the  lower  it  also  descends;  the  fibers  of  the  articular  capsule  are  relaxed  in  a  vertical  direc- 
tion, and  will  then  permit  of  movement  in  an  antero-posterior  direction.  By  this  means  a 
shorter  capsule  suffices  and  the  strength  of  the  joint  is  materially  increased.^ 

This  joint  allows  the  rotation  of  the  atlas  (and,  with  u,  the  skull)  upon  the  axis,  the  extent 
of  rotation  being  hmited  by  the  alar  hgaments. 

The  principal  muscles  by  which  these  movements  are  produced  are  the  Sternocleidomastoideus 
and  Semispinalis  capitis  of  one  side,  acting  with  the  Longus  capitis,  Splenius,  Longissimus  capitis, 
Rectus  capitis  posterior  major,  and  Obliqui  capitis  superior  and  inferior  of  the  other  side. 


n 


in.    Articulations  of  the  Vertebral  Column  with  the  Cranium. 


II 


The  ligaments  connecting  the  vertebral  column  with  the  cranium  may  be 
divided  into  two  sets:  those  uniting  the  atlas  with  the  occipital  bone,  and  those 
connecting  the  axis  with  the  occipital  bone. 

Articulation  of  the  Atlas  with  the  Occipital  Bone  (articulatio  atlantodccipitalis). 
■ — The  articulation  between  the  atlas  and  the  occipital  bone  consists  of  a  pair  of 
condyloid  joints.    The  ligaments  connecting  the  bones  are: 

Two  Articular  Capsules.  The  Posterior  Atlantooccipital 

The  Anterior  Atlantooccipital  membrane. 

membrane.  Two  Lateral  Atlantooccipital. 

The  Articular  Capsules  {capsulcB  articulares;  capsular  ligaments). — The  articular 
capsules  surround  the  condyles  of  the  occipital  bone,  and  connect  them  with  the 
articular  processes  of  the  atlas :  they  are  thin  and  loose. 

The  Anterior  Atlantooccipital  Membrane  (membrana  atlantodccipitalis  anterior; 
anterior  atlantooccipital  ligament)  (Fig.  304). — The  anterior  atlantooccipital  mem- 
brane is  broad  and  composed  of  densely  woven  fibers,  which  pass  between  the 
anterior  margin  of  the  foramen  magnum  above,  and  the  upper  border  of  the 
anterior  arch  of  the  atlas  below;  laterally,  it  is  continuous  with  the  articular 
capsules;  in  front,  it  is  strengthened  in  the  middle  line  by  a  strong,  rounded 

'  Comer  ("The  Physiology  of  the  Atlanto-axial  Joints,"  Journal  of  Anatomj'  and  Physiology,  vol.  xli)  states  that 
the  movements  which  take  place  at  these  articulations  are  of  a  complex  nature.  The  first  part  of  the  movement  is 
.an  eccentric  or  asymmetrical  one;  the  atlanto-axial  joint  of  the  side  to  which  the  head  is  moved  is  fixed,  or  practically 
fixed,  by  the  muscles  of  the  neck,  and  forms  the  center  of  the  movement,  while  the  opposite  atlantal  facet  is  carried 
downward  and  forward  on  the  corresponding  axial  facet.  The  second  part  of  the  movement  is  centric  and  symmetrical, 
the  odontoid  process  forming  the  axis  of  the  movement 


296  J^^^^^.  SYNDESMOLOGY 


ll 


cord,  which  connects  the  basilar  part  of  the  occipital  bone  to  the  tubercle  on  tli€ 
anterior  arch  of  the  atlas.  This  membrane  is  in  relation  in  front  with  the  Recti 
capitis  anteriores,  behind  with  the  alar  ligaments. 

The  Posterior  Atlantobccipital  Membrane  (membrana  atlantooccipitalis  posterior; 
posterior  atlantooccipital  ligament)  (Fig.  305) . — The  posterior  atlantooccipital  mem- 
brane, broad  but  thin,  is  connected  above,  to  the  posterior  margin  of  the  foramen 
magnum;  below,  to  the  upper  border  of  the  posterior  arch  of  the  atlas.    On  either  ^_ 
side  this  membrane  is  defective  below,  over  the  groove  for  the  vertebral  artery,  ^M 
and  forms  with  this  groove  an  opening  for  the  entrance  of  the  artery  and  the 
exit  of  the  suboccipital  nerve.    The  free  border  of  the  membrane,  arching  over 
the  artery  and  nerve,  is  sometimes  ossified.     The  membrane  is  in  relation,  behind, 
with  the  Recti  capitis  posteriores  minores  and  Obliqui  capitis  superiores ;  in  fronts  ^h 
with  the  dura  mater  of  the  vertebral  canal,  to  which  it  is  intimately  adherent.         ^M 

The  Lateral  Ligaments. — The  lateral  ligaments  are  thickened  portions  of  the 
articular  capsules,  reinforced  by  bundles  of  fibrous  tissue,  and  are  directed  obliquely 
upward  and  medialward;  they  are  attached  above  to  the  jugular  processes  of  the 
occipital  bone,  and  below,  to  the  bases  of  the  transverse  processes  of  the  atlas. 

Synovial  Membranes. — There  are  two  synovial  membranes:  one  lining  each  of  the  articular 
capsules.  The  joints  frequently  communicate  with  that  between  the  posterior  siuface  of  the 
odontoid  process  and  the  transverse  ligament  of  the  atlas. 

Movements. — The  movements  permitted  in  this  joint  are  (a)  flexion  and  extension,  which 
give  rise  to  the  ordinary  forward  and  backward  nodding  of  the  head,  and  (6)  slight  lateral  motion 
to  one  or  other  side.  Flexion  is  produced  mainly  by  the  action  of  the  Longi  capitis  and  Recti 
capitis  anteriores;  extension  by  the  Recti  capitis  posteriores  major  and  minor,  the  Obliquus  su- 
perior, the  SemispinaUs  capitis,  Splenius  capitis,  Sternocleidomastoideus,  and  upper  fibers  of  the 
Trapezius.  The  Recti  laterales  are  concerned  in  the  lateral  movement,  assisted  by  the  Trapezius, 
Splenius  capitis,  Semispinalis  capitis,  and  the  Sternocleidomastoideus  of  the  same  side,  all  acting 
together. 

Ligaments  Connecting  the  Axis  with  the  Occipital  Bone. — 

The  Membrana  Tectoria.  Two  Alar.  The  Apical  Odontoid. 

The  Membrana  Tectoria  (occipitoaxial  ligament)  (Figs.  307,  308). — The  mem- 
brana tectoria  is  situated  within  the  vertebral  canal.  It  is  a  broad,  strong  bands 
which  covers  the  odontoid  process  and  its  ligaments,  and  appears  to  be  a  prolon- 
gation upward  of  the  posterior  longitudinal  ligament  of  the  vertebral  column.  It 
is  fixed,  below,  to  the  posterior  surface  of  the  body  of  the  axis,  and,  expanding  as 
it  ascends,  is  attached  to  the  basilar  groove  of  the  occipital  bone,  in  front  of  the 
foramen  magnum,  where  it  blends  with  the  cranial  dura  mater.  Its  anterior  sur- 
face is  in  relation  with  the  transverse  ligament  of  the  atlas,  and  its  posterior 
surface  with  the  dura  mater. 

The  Alar  Ligaments  (ligamenta  alaria;  odontoid  ligaments)  (Fig.  307). — The  alar 
ligaments  are  strong,  rounded  cords,  which  arise  one  on  either  side  of  the  upper 
part  of  the  odontoid  process,  and,  passing  obliquely  upward  and  lateralward,  are 
inserted  into  the  rough  depressions  on  the  medial  sides  of  the  condyles  of  the  occipi- 
tal bone.  In  the  triangular  interval  between  these  ligaments  is  another  fibrous 
cord,  the  apical  odontoid  ligament  (Fig.  308),  which  extends  from  the  tip  of  the  odon- 
toid process  to  the  anterior  margin  of  the  foramen  magnum,  being  intimately 
blended  with  the  deep  portion  of  the  anterior  atlantooccipital  membrane  and 
superior  crus  of  the  transverse  ligament  of  the  atlas.  It  is  regarded  as  a  rudimentary 
intervertebral  fibrocartilage,  and  in  it  traces  of  the  notochord  may  persist.  The 
alar  ligaments  limit  rotation  of  the  cranium  and  therefore  receive  the  name  of 
check  ligaments. 

In  addition  to  the  ligaments  which  unite  the  atlas  and  axis  to  the  skull, 
the  ligamentum  nuchse  (page  290)  must  be  regarded  as  one  of  the  ligaments 
connecting  the  vertebral  column  with  the  cranium. 


ARTICULATION  OF  THE  MANDIBLE 


297 


rv.     Articulation  of  the  Mandible  (Articulatio  Mandibularis ;  Temporo- 
mandibular Articulation). 

This  is  a  ginglymo-arthrodial  joint;  the  parts  entering  into  its  formation  on 
either  side  are:  the  anterior  part  of  the  mandibular  fossa  of  the  temporal  bone 
and  the  articular  tubercle  above;  and  the  condyle  of  the  mandible  below.  The 
ligaments  of  the  joint  are  the  following: 

The  Articular  Capsule.  The  Sphenomandibular. 

The  Temporomandibular.  The  Articular  Disk. 

The  Stylomandibular. 

The  Articular  Capsule  (capsula  articularis;  capsular  ligament). — The  articular 
capsule  is  a  thin,  loose  envelope,  attached  above  to  the  circumference  of  the 
mandibular  fossa  and  the  articular  tubercle  immediately  in  front;  below,  to  the 
neck  of  the  condyle  of  the  mandible. 


Fig.  309. — Articulation  of  the  mandible.     Lateral  aspect. 


I 


le  Temporomandibular  Ligament  (ligamentum  temporomandibulare;  external 
lateral  ligament)  (Fig.  309).— The  temporomandibular  ligament  consists  of  two 
short,  narrow  fasciculi,  one  in  front  of  the  other,  attached,  above,  to  the  lateral 
surface  of  the  zygomatic  arch  and  to  the  tubercle  on  its  lower  border;  below, 
to  the  lateral  surface  and  posterior  border  of  the  neck  of  the  mandible.  It  is  broader 
above  than  below,  and  its  fibers  are  directed  obliquely  downward  and  backward. 
It  is  covered  by  the  parotid  gland,  and  by  the  integument. 

The  Sphenomandibular  Ligament  (ligamentum  sphenomandibulare;  internal  lateral 
ligament)  (Fig.  310). — The  sphenomandibular  ligament  is  a  flat,  thin  band  which  is 
attached  above  to  the  spina  angularis  of  the  sphenoid  bone,  and,  becoming  broader 
as  it  descends,  is  fixed  to  the  lingula  of  the  mandibular  foramen.  Its  lateral  surface 
is  in  relation,  above,  with  the  Pterygoideus  externus;  lower  down,  it  is  separated 
from  the  neck  of  the  condyle  by  the  internal  maxillary  vessels;  still  lower,  the 
inferior  alveolar  vessels  and  nerve  and  a  lobule  of  the  parotid  gland  lie  between 
it  and  the  ramus  of  the  mandible.  Its  medial  surface  is  in  relation  with  the  Ptery- 
goideus internus. 


298 


SYNDESMOLOGY 


The  Articular  Disk  (discus  articularis;  interarticular  fihrocartilage ;  articular  menS 
cus)  (Fig.  311).— The  articular  disk  is  a  thin,  oval  plate,  placed  between  the 
condyle  of  the  mandible  and  the  mandibular  fossa.  Its  upper  surface  is  concavo-j 
convex  from  before  backward,  to  accommodate  itself  to  the  form  of  the  man- 
dibular fossa  and  the  articular  tubercle.  Its  under  surface,  in  contact  with  the 
condyle,  is  concave.  Its  circumference  is  connected  to  the  articular  capsule;  and  in 
front  to  the  tendon  of  the  Pterygoideus  externus.  It  is  thicker  at  its  periphery, 
especially  behind,  than  at  its  center.  The  fibers  of  which  it  is  composed  have  a 
concentric  arrangement,  more  apparent  at  the  circumference  than  at  the  center. 
It  divides  the  joint  into  two  cavities,  each  of  which  is  furnished  with  a  synovial 
membrane. 


Fig.  310. — ^Articulation  of  the  mandible.     Medial  aspect. 


Fig. 


311. — Sagittal  section  of  the  articulation  of  the 
mandible. 


The  Synovial  Membranes. — The  synovial  membranes,  two  in  number,  are  placed  one  above, 
and  the  other  below,  the  articular  disk.  The  upper  one,  the  larger  and  looser  of  the  two,  ia 
continued  from  the  margin  of  the  cartilage  covering  the  mandibular  fossa  and  articular  tubercle 
on  to  the  upper  surface  of  the  disk.  The  lower  one  passes  from  the  under  surface  of  the  disk 
to  the  neck  of  the  condyle,  being  prolonged  a  little  farther  downward  behind  than  in  front.  The 
articular  disk  is  sometimes  perforated  in  its  center,  and  the  two  cavities  then  communicate  with 
each  other. 

The  Stylomandibular  Ligament  {ligamentum  stylomandihulare) ;  stylomaxillary 
ligament  (Fig.  310). — The  stylomandibular  ligament  is  a  specialized  band  of  the 
cervical  fascia,  which  extends  from  near  the  apex  of  the  styloid  process  of  the 
temporal  bone  to  the  angle  and  posterior  border  of  the  ramus  of  the  mandible, 
between  the  Masseter  and  Pterygoideus  internus.  This  ligament  separates  the 
parotid  from  the  submaxillary  gland,  and  from  its  deep  surface  some  fibers  of  the 
Styloglossus  take  origin.  Although  classed  among  the  ligaments  of  the  temporo- 
mandibular joint,  it  can  only  be  considered  as  accessory  to  it. 

The  nerves  of  the  temporomandibular  joint  are  derived  from  the  auriculotemporal  and  masse- 
teric branches  of  the  mandibular  nerve,  the  arteries  from  the  superficial  temporal  branch  of  the 
external  carotid. 

Movements. — The  movements  permitted  in  this  articulation  are  extensive.  Thus,  the  mandible 
may  be  depressed  or  elevated,  or  carried  forward  or  backward;  a  slight  amount  of  side-to-side 
movement  is  also  permitted.  It  must  be  borne  in  mind  that  there  are  two  distinct  joints  in  this 
articulation — one  between  the  condyle  and  the  articular  disk,  and  another  between  the  disk  and 
the  mandibular  fossa.    When  the  mouth  is  but  sUghtly  opened,  as  during  ordinary  conversation, 


COSTOVERTEBRAL  ARTICULATIONS  299 

the  movement  is  confined  to  the  lower  of  the  two  joints.  On  the  other  hand,  when  the  mouth 
is  opened  more  widely,  both  joints  are  concerned  in  the  movement;  in  the  lower  joint  the  move- 
ment is  of  a  hinge-Uke  character,  the  condyle  moving  around  a  transverse  axis  on  the  disk,  while 
in  the  upper  joint  the  movement  is  of  a  ghding  character,  the  disk,  together  with  the  condyle, 
gUding  forward  on  to  the  articular  tubercle,  around  an  axis  which  passes  through  the  mandibular 
foramina.  These  two  movements  take  place  simultaneously,  the  condyle  and  disk  move  for- 
ward on  the  eminence,  and  at  the  same  time  the  condyle  revolves  on  the  disk.  In  shutting  the 
mouth  the  reverse  action  takes  place;  the  disk  glides  back,  carrying  the  condyle  with  it,  and  this 
at  the  same  time  moves  back  to  its  former  position.  When  the  mandible  is  carried  horizontally 
forward,  as  in  protruding  the  lower  incisor  teeth  in  front  of  the  upper,  the  movement  takes  place 
principally  in  the  upper  joint,  the  disk  and  the  condyle  gUding  forward  on  the  mandibular  fossa 
and  articular  tubercle.  The  grinding  or  chewing  movement  is  produced  by  one  condyle,  with 
its  disk,  gUding  alternately  forward  and  backward,  while  the  other  condyle  moves  simultaneously 
in  the  opposite  direction;  at  the  same  time  the  condyle  undergoes  a  vertical  rotation  on  the  disk. 
One  condyle  advances  and  rotates,  the  other  condyle  recedes  and  rotates,  in  alternate  succession. 
The  mandible  is  depressed  by  its  own  weight,  assisted  by  the  Platysma,  the  Digastricus,  the 
Mylohyoideus,  and  the  Geniohyoideus.  It  is  elevated  by  the  Masseter,  Pterygoideus  internus, 
and  the  anterior  part  of  the  Temporalis.  It  is  drawn  forward  by  the  simultaneous  action  of  the 
Pterygoidei  internus  and  externus,  the  superficial  fibers  of  the  Masseter  and  the  anterior  fibers 
of  the  Temporalis;  and  backward  by  the  deep  fibers  of  the  Masseter  and  the  posterior  fibers  of  the 
Temporalis.  The  grinding  movement  is  caused  by  the  alternate  action  of  the  Pterygoidei  of 
either  side. 


IT 


V.    Costovertebral  Articulations  (Articulationes  Costovertebrales). 

The  articulations  of  the  ribs  with  the  vertebral  column  may  be  divided  into  two 
sets,  one  connecting  the  heads  of  the  ribs  with  the  bodies  of  the  vertebrae,  another 
uniting  the  necks  and  tubercles  of  the  ribs  with  the  transverse  processes. 

1 ,  Articulations  of  the  Heads  of  the  Ribs  (articulationes  capitulorum;  costocentral 
articulations)  (Fig.  312). — These  constitute  a  series  of  gliding  or  arthrodial  joints, 
and  are  formed  by  the  articulation  of  the  heads  of  the  typical  ribs  with  the  facets 
on  the  contiguous  margins  of  the  bodies  of  the  thoracic  vertebrae  and  with  the 
intervertebral  fibrocartilages  between  them;  the  first,  tenth,  eleventh,  and  twelfth 

I  ribs  each  articulate  with  a  single  vertebra.    The  ligaments  of  the  joints  are: 
I    The  Articular  Capsule.  The  Radiate.  The  Interarticular. 

'  The  Articular  Capsule  (capsula  articularis;  capsular  ligament). — The  articular 
capsule  surrounds  the  joint,  being  composed  of  short,  strong  fibers,  connecting 
the  head  of  the  rib  with  the  circumference  of  the  articular  cavity  formed  by  the 
intervertebral  fibrocartilage  and  the  adjacent  vertebrae.  It  is  most  distinct  at 
the  upper  and  lower  parts  of  the  articulation ;  some  of  its  upper  fibers  pass  through 
the  intervertebral  foramen  to  the  back  of  the  intervertebral  fibrocartilage,  while 
its  posterior  fibers  are  continuous  with  the  ligament  of  the  neck  of  the  rib. 

The  Radiate  Ligament  (ligamentum  capituli  costce  radiatum;  anterior  costoverte- 
bral or  stellate  ligament). — The  radiate  ligament  connects  the  anterior  part  of  the 
head  of  each  rib  with  the  side  of  the  bodies  of  two  vertebrae,  and  the  interverte- 
bral fibrocartilage  between  them.  It  consists  of  three  flat  fasciculi,  which  are 
attached  to  the  anterior  part  of  the  head  of  the  rib,  just  beyond  the  articular  sur- 
face. The  superior  fasciculus  ascends  and  is  connected  with  the  body  of  the  verte- 
bra above ;  the  inferior  one  descends  to  the  body  of  the  vertebra  below ;  the  middle 
one,  the  smallest  and  least  distinct,  is  horizontal  and  is  attached  to  the  interver- 
tebral fibrocartilage.  The  radiate  ligament  is  in  relation,  in  front,  with  the  thoracic 
ganglia  of  the  sympathetic  trunk,  the  pleura,  and,  on  the  right  side,  with  the  azygos 
vein;  behind,  with  the  interarticular  ligament  and  synovial  membranes. 

In  the  case  of  the  first  rib,  this  ligament  is  not  divided  into  three  fasciculi,  but 
its  fibers  are  attached  to  the  body  of  the  last  cervical  vertebra,  as  well  as  to  that 
of  the  first  thoracic.  In  the  articulations  of  the  heads  of  the  tenth,  eleventh,  and 
twelfth  ribs,  each  of  which  articulates  with  a  single  vertebra,  the  triradiate  arrange- 


300 


SYNDESMOLOGY 


ment  does  not  exist;  but  the  fibers  of  the  ligament  in  each  case  are   connecteic 
the  vertebra  above,  as  well  as  to  that  with  which  the  rib  articulates. 

The  Interarticular  Ligament  {ligavientum  capituli  costcc  interarticulare) . — The  in- 
terarticular  ligament  is  situated  in  the  interior  of  the  joint.  It  consists  of  a  short 
band  of  fibers,  flattened  from  above  downward,  attached  by  one  extremity  to  the 
crest  separating  the  two  articular  facets  on  the  head  of  the  rib,  and  by  the  other 
to  the  intervertebral  fibrocartilage;  it  divides  the  joint  into  two  cavities.  In  the 
joints  of  the  first,  tenth,  eleventh,  and  twelfth  ribs,  the  interarticular  ligament  does 
not  exist;  consequently,  there  is  but  one  cavity  in  each  of  these  articulations. 
This  ligament  is  the  homologue  of  the  ligamentum  conjugale  present  in  some 
mammals,  and  uniting  the  heads  of  opposite  ribs,  across  the  back  of  the  inter- 
vertebral fibrocartilage. 


Anterior 

costotransverse 

ligaments 


Jnterarticidar  ligament  Intervertebral  fibrocartilage 

Fig.  312. — Costovertebral  articulations.     Anterior  view. 


«ll 


Synovial  Membranes. — There  are  two  synovial  membranes  in  each  of  the  articulations  where 
an  interarticular  ligament  exists,  one  above  and  one  below  this  structure;  but  only  one  in  those 
joints  where  there  are  single  cavities. 

2.  Costotransverse  Articulations  (articulationes  costotransversaricB)  (Fig.  313). — 
The  articular  portion  of  the  tubercle  of  the  rib  forms  with  the  articular  surface 
on  the  adjacent  transverse  process  an  arthrodial  joint. 

In  the  eleventh  and  twelfth  ribs  this  articulation  is  wanting. 
The  ligaments  of  the  joint  are : 

The  Articular  Capsule.  The  Posterior  Costotransverse. 

The  Anterior  Costotransverse.  The  Ligament  of  the  Neck  of  the  Rib. 

The  Ligament  of  the  Tubercle  of  the  Rib. 


COSTOVERTEBRAL  ARTICULATIONS 


301 


The  Articular  Capsule  (capsula  articularis;  capsular  ligament). — ^The  articular  cap- 
sule is  a  thin  membrane  attached  to  the  circumferences  of  the  articular  surfaces, 
.and  lined  by  a  synovial  membrane. 


/Synovial  cavity 


Anterior  costotransverse 
ligament  divided, 

Ligament  of  the  neck 

Ligament  of  the 
tubercle 


Fig.  313. — Costotransverse  articulation.     Seen  from  above. 

The  Anterior  Costotransverse  Ligament  (liga- 
mentum  costotransversarium  anterius;  anterior 
superior  ligament). — The  anterior  costotrans- 
verse ligament  is  attached  below  to  the  sharp 
crest  on  the  upper  border  of  the  neck  of  the 
rib,  and  passes  obliquely  upward  and  lateral- 
ward  to  the  lower  border  of  the  transverse 
process  immediately  above.  It  is  in  relation, 
in  front,  with  the  intercostal  vessels  and 
nerves;  its  medial  border  is  thickened  and 
free,  and  bounds  an  aperture  which  transmits 
the  posterior  branches  of  the  intercostal  vessels 
and  nerves;  its  lateral  border  is  continuous 
with  a  thin  aponeurosis,  which  covers  the 
Intercostalis  externus. 

The